explain xkcd - User contributions [en]

Talk:1252: Increased Risk

2013-08-17T18:15:58Z

CFoxx:

I think this is to address the old chestnut of "<something> will ''double'' your risk of getting cancer!", or the like, where the risk of getting that cancer (in this example) is maybe 1 in 10,000, so doubling the risk across a population wouldmake that a 1 in 5,000 risk to your health... which you may still consider to be an acceptable gamble if it's something nice (like cheese!) that's apaprently to blame and you'd find abstinence from it gives a barely marginal benefit for a far greater loss of life enjoyment. Also, this sort of figure almost always applies towards a ''specific form'' of cancer, or whatever risk is being discussed, meaning you aren't vastly changing your life expectancy at all. In fact, the likes of opposing "red wine is good/bad for you" studies can be mutually true by this same principle (gain a little risk of one condition, lose a little risk from another). (Note: I don't know of any particular "cheese gives you cancer!" stories doing the rounds, at the moment. I bet they have done, but I only mention it because I actually quite like cheese. And I probably ''wouldn't'' give it up under the above conditions.)

It's also possible that this covers the likes of "<foo> in <country> is 10 times more dangerous than it is <other country>" statements. Perhaps ''only'' ten incidents happened in the former, and a single instance in the latter, out the ''whole'' of each respective country. Or a single incident occured in both, but the second country is ten times the size, so gets 'adjusted for population' in the tables. And, besides which, that was just for one year and was just a statistical blip that will probably revert-towards-the-mean next year.

Finally, for a given risk of some incident happening on the first two trips, with no 'memory' or build-up involved, it pretty much is half-as-likely-again for the incident to have happened (some time!) in three separate trips. (Not quite, if those that lose against the odds and get caught by the incident the first or second trip never get to ''have'' a (second or) third trip... but for negligable odds like thegiven example, of the dog with the handgun, it's near-as-damnit so.) [[Special:Contributions/178.104.103.140|178.104.103.140]] 11:12, 16 August 2013 (UTC)

Where did "dogs with shotguns" come from? I only saw "handgun" in the comic. Besides, I interpreted the risk as being hit by a negligent discharge from the handgun, not being deliberately attacked by the dog. Also, since probabilities are the set of real numbers between 0 and 1 inclusive, there are an uncountable number of them. "A x% increase in a tiny risk is still tiny" is an inductive statement, which means it could only be used to argue that a countable set of numbers is tiny. [[Special:Contributions/76.64.65.200|76.64.65.200]] 12:24, 16 August 2013 (UTC)

:If induction base is uncountable, you can prove it for the whole [0; 1]. For example your induction base may be "every risk under 0.00000000000000000001% is tiny". --[[User:DiEvAl|DiEvAl]] ([[User talk:DiEvAl|talk]]) 12:38, 16 August 2013 (UTC)

I think it's worth mentioning that this comic doesn't [[985|distinguish between percentages and percentage points]]. --[[User:DiEvAl|DiEvAl]] ([[User talk:DiEvAl|talk]]) 12:35, 16 August 2013 (UTC)

Is it the case that doing something three times increases risk by 50% over two times inherently? I feel like this is the case, but it's early, here. Also, I'm not sure Randall is attacked by a dog, he may be using it as a diversion. I think that he's done this before. [[User:Theo|Theo]] ([[User talk:Theo|talk]]) 12:56, 16 August 2013 (UTC)
:(First, good point, DiEvAl, about the percentages/percentage-points. I ''knew'' I'd missed something out in my first thoughts. I actually tend to assume ''against'' percentage points, which is somewhat the opposite from what I've seen in the general public.)
:Actually, depends on how you count it. But I was using the "encounter 'n' incidents per trip", "encounter '2n' incidents per two trips", "encoutner '3n' incidents per three trips" measure, where 3n==2n+50%. But that works best with a baseline of >>1 incidents per trip assumed. In reality, if the chance is a fractional 'p' for an occurance in one instance, it's (1-p) that it ''didn't'' occur thus (1-p)n that it didn't occur in any of 'n' instances and 1-(1-p)n that it did (at least once, possible several times or even all). Not so simple, but for p tending to zero it 'does' converge on 1.5 times for across three what you'd expect for two (albeit because 0*1.5=0). Like they say, "Lies, Damn Lies...", etc. ;) [[Special:Contributions/178.104.103.140|178.104.103.140]] 14:22, 16 August 2013 (UTC)

I don't think Randall is being attacked by a dog at all. What he's saying is that if you are going to think getting attacked by a shark is so likely, then you better be watching out for that never-gonna-happen dog scenario too. [[User:Jillysky|Jillysky]] ([[User talk:Jillysky|talk]]) 13:56, 16 August 2013 (UTC)

Is 0.000001% really "one in a million"?
;If 1% = 1 in 100, then
:0.1% = 1 in a 1,000
:0.01% = 1 in a 10,000
:0.001% = 1 in a 100,000
:0.0001% = 1 in a 1,000,000
:0.00001% = 1 in a 10,000,000
:'''0.000001% = 1 in a 100,000,000'''
Would it be more accurate to leave off the % sign?
Assuming I'm right, I think it'd be less confusing to leave it and reduce the numbers by a couple orders of magnitude.
--Clayton [[Special:Contributions/12.202.74.87|12.202.74.87]] 14:36, 16 August 2013 (UTC)

''If the chance of the dog attack is 0.000000001% (one in a billion) on each visit to the beach, then the chance of attack over two visits is 0.000000002% whereas in three visits it becomes 0.000000003%''

Um, no. Following that logic, if I go to the beach a billion times then I '''will''' get shot by a dog that is packing. Rather, each visit to the beach has it's own odds, like the rolling of dice? On any particular visit there's a one-in-a-billion chance. And that's true on each subsequent visit as well. Tuesday's visit to the beach isn't twice as dangerous just because I was at the beach on Monday. [[User:CFoxx|CFoxx]] ([[User talk:CFoxx|talk]]) 16:26, 16 August 2013 (UTC)
:For each visit that is the case. Because it's one visit, that's true. However, if (time not being a factor) one were to have a billion visits planned, the odds over all would be increased. Pretty sure that overall this means that you got the joke faster than I did. Thanks for the clarification! [[User:Theo|Theo]] ([[User talk:Theo|talk]]) 17:06, 16 August 2013 (UTC)
::The odds overall may increase with multiple visits. But not, at least, at the rate listed. Otherwise that billionth trip (if one survived that long as one is likely to do) would be certain death. [[User:CFoxx|CFoxx]] ([[User talk:CFoxx|talk]]) 17:30, 16 August 2013 (UTC)
:::Correct. Technically, the odds we are worried about are the "probability of being shot one or more times by a dog". So if the probability is 1/10^9 for any given day, than the odds of not being shot are (10^9-1)/10^9 for any given day, and the odds of not being shot over three days are (10^9-1)^3/10^27, and then the odds of being shot one or more times are 1-((10^9-1)^3/10^27), which is roughly 2.999999997000000001/10^9. That is close, but slightly less, than 3/10^9. [[Special:Contributions/206.174.12.203|206.174.12.203]] 18:01, 16 August 2013 (UTC)Toby Ovod-Everett
::::Absolute incorrect: You always have to look at the single event. More events do not belong together, you always have the same probability at each single event. So, even 10 billion events may or may NOT result in a disaster. Math isn't easy.--[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 19:17, 16 August 2013 (UTC)
:::::I believe what CFoxx was saying is that if the odds of something happening on any given day are one in three, then the odds of that thing happening at least once during a four day period is NOT 4/3rds! I was pointing out that the proper way to calculate the odds for a four day period is to say that the odds of it not happening on any given day are two in three. You take that probability and raise it to the fourth power, giving the odds that it won't happen at all during a four day period of 16/81, thus the odds that it will happen during that four day period is 65/81. I then did that same calculation for the 1 in a billion chance per day and applied it to the three day period, and recognized that he was correct that the true probability of the event happening one or more times over a three day period was not three times the probability of it happening on any given day, but also noted that the difference for a 1 in a billion chance over a small period is pretty close to the simplistic (but incorrect) approach. My rough estimate for the "one in a billion per day" event happening one or more times during a billion day period is 63.21%.[[Special:Contributions/206.174.12.203|206.174.12.203]] 21:33, 16 August 2013 (UTC)Toby Ovod-Everett
::::::Wow, we still have many great scientists here!--[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 21:46, 16 August 2013 (UTC)
::::::THANK YOU, Toby! [[User:CFoxx|CFoxx]] ([[User talk:CFoxx|talk]]) 18:09, 17 August 2013 (UTC)

Just a thought: is the title text a reference to the Sorites paradox? --AJ [[Special:Contributions/80.42.221.105|80.42.221.105]] 17:25, 16 August 2013 (UTC)

Rats! I made the newbie mistake of editing something before I found the discussion page. I looked for it, honest I did! I see that UTC has already brought up what I referred to as "Cueball's error" in my (pre-log-in) edit. I did find it hard to believe I'd be the first xkcd fan to notice this error. I think this is worth addressing in the explanation, though I of course won't take offense if someone wants to obliterate my edit and start over. (CLSI){{unsigned|CLSI}}

Maybe he means this: Florida man shot by his dog, police say http://usnews.nbcnews.com/_news/2013/02/26/17107343-florida-man-shot-by-his-dog-police-say?lite{{unsigned|Jb}}

Saying that unfortunately Cueball is mistaken in his calculations because he said 50% instead of 49.99999992% is a bit of an exaggeration. [[User:Xhfz|Xhfz]] ([[User talk:Xhfz|talk]]) 20:19, 16 August 2013 (UTC)

;Chaos at explain section
Please stop adding this, it does not explain the comic, it only belongs to this discussion page:

:Note that the 50% figure is an approximation. Assuming the odds of being attacked by a dog is ''x'', the odds of being attacked by a dog at least once in two visits is 1 - (1-''x'')2. The odds of being attacked at least once in three visits is 1 - (1-''x'')3. Therefore, if one visit has one in a billion probability of attack, then two visits have not 2 in a billion, but 1.999999999 in a billion. Similarly, three visits have a probability of 2.999999997 in a billion. Saying 50% instead of 49.99999992% is a reasonable approximation.

:Unfortunately, [[Cueball]] is mistaken in his calculations. This is easier to see with an event that has greater probability, such as a coin toss. Assuming the odds of getting heads in one flip is .5, the odds of getting heads at least once in two flips is .75 (i.e., 1 minus [.5 X .5], the odds of getting tails both times), and the odds of getting heads at least once in three flips is .875 (1 minus [.5 X .5 X .5], the odds of getting three tails in a row). Getting heads in three flips is not 50% more likely than getting heads in two flips. With very low probabilities (such as the probability of attack by a dog swimming with a handgun), Cueball's calculation gives an extremely close approximation of the actual probability, but one can't apply the same logic to events of just any probability.

::Cueball says *statistically* the risk of some bizarre event increases 50%. This is essentially correct as many have pointed out that 49.99999999 is not really statistically different than 50. What is likely bothering a lot of people (including myself) is that the explainxkcd description states "If the chance of the dog attack is one per billion on each visit to the beach, then the chance of attack over two visits *is* two per billion whereas in three visits it *becomes* three per billion." There are no weasel words like "approximately", "about", "around", etc. This reminds people of flatly incorrect uses of probabilities like the one you describe. But surely the probability of getting heads from a fair coin toss is not on a similar order of magnitude as the probability that a swimming dog shoots someone with a handgun. [[User:S|S]] ([[User talk:S|talk]]) 00:40, 17 August 2013 (UTC)
:::''What is likely bothering a lot of people (including myself) is that the explainxkcd description states "If the chance of the dog attack is one per billion on each visit to the beach, then the chance of attack over two visits *is* two per billion whereas in three visits it *becomes* three per billion." There are no weasel words like "approximately", "about", "around", etc.'' '''Exactly.''' Explanations here have been very helpful in explaining some of the more scientific aspects of things Randall includes. Noting this one makes a (albeit slight) mistake in that regard is appropriate. (And the irony of incorrectly using probabilities in explaining a comic about how people do that is amusing.) [[User:CFoxx|CFoxx]] ([[User talk:CFoxx|talk]]) 18:15, 17 August 2013 (UTC)

I had to think of http://xkcd.com/1102/ when reading the first paragraph of the explainxkcd description. (The context is different, but the dubious use of percentages is the same.) [[User:S|S]] ([[User talk:S|talk]]) 00:40, 17 August 2013 (UTC)

Talk:1252: Increased Risk

2013-08-17T18:09:19Z

CFoxx:

I think this is to address the old chestnut of "<something> will ''double'' your risk of getting cancer!", or the like, where the risk of getting that cancer (in this example) is maybe 1 in 10,000, so doubling the risk across a population wouldmake that a 1 in 5,000 risk to your health... which you may still consider to be an acceptable gamble if it's something nice (like cheese!) that's apaprently to blame and you'd find abstinence from it gives a barely marginal benefit for a far greater loss of life enjoyment. Also, this sort of figure almost always applies towards a ''specific form'' of cancer, or whatever risk is being discussed, meaning you aren't vastly changing your life expectancy at all. In fact, the likes of opposing "red wine is good/bad for you" studies can be mutually true by this same principle (gain a little risk of one condition, lose a little risk from another). (Note: I don't know of any particular "cheese gives you cancer!" stories doing the rounds, at the moment. I bet they have done, but I only mention it because I actually quite like cheese. And I probably ''wouldn't'' give it up under the above conditions.)

It's also possible that this covers the likes of "<foo> in <country> is 10 times more dangerous than it is <other country>" statements. Perhaps ''only'' ten incidents happened in the former, and a single instance in the latter, out the ''whole'' of each respective country. Or a single incident occured in both, but the second country is ten times the size, so gets 'adjusted for population' in the tables. And, besides which, that was just for one year and was just a statistical blip that will probably revert-towards-the-mean next year.

Finally, for a given risk of some incident happening on the first two trips, with no 'memory' or build-up involved, it pretty much is half-as-likely-again for the incident to have happened (some time!) in three separate trips. (Not quite, if those that lose against the odds and get caught by the incident the first or second trip never get to ''have'' a (second or) third trip... but for negligable odds like thegiven example, of the dog with the handgun, it's near-as-damnit so.) [[Special:Contributions/178.104.103.140|178.104.103.140]] 11:12, 16 August 2013 (UTC)

Where did "dogs with shotguns" come from? I only saw "handgun" in the comic. Besides, I interpreted the risk as being hit by a negligent discharge from the handgun, not being deliberately attacked by the dog. Also, since probabilities are the set of real numbers between 0 and 1 inclusive, there are an uncountable number of them. "A x% increase in a tiny risk is still tiny" is an inductive statement, which means it could only be used to argue that a countable set of numbers is tiny. [[Special:Contributions/76.64.65.200|76.64.65.200]] 12:24, 16 August 2013 (UTC)

:If induction base is uncountable, you can prove it for the whole [0; 1]. For example your induction base may be "every risk under 0.00000000000000000001% is tiny". --[[User:DiEvAl|DiEvAl]] ([[User talk:DiEvAl|talk]]) 12:38, 16 August 2013 (UTC)

I think it's worth mentioning that this comic doesn't [[985|distinguish between percentages and percentage points]]. --[[User:DiEvAl|DiEvAl]] ([[User talk:DiEvAl|talk]]) 12:35, 16 August 2013 (UTC)

Is it the case that doing something three times increases risk by 50% over two times inherently? I feel like this is the case, but it's early, here. Also, I'm not sure Randall is attacked by a dog, he may be using it as a diversion. I think that he's done this before. [[User:Theo|Theo]] ([[User talk:Theo|talk]]) 12:56, 16 August 2013 (UTC)
:(First, good point, DiEvAl, about the percentages/percentage-points. I ''knew'' I'd missed something out in my first thoughts. I actually tend to assume ''against'' percentage points, which is somewhat the opposite from what I've seen in the general public.)
:Actually, depends on how you count it. But I was using the "encounter 'n' incidents per trip", "encounter '2n' incidents per two trips", "encoutner '3n' incidents per three trips" measure, where 3n==2n+50%. But that works best with a baseline of >>1 incidents per trip assumed. In reality, if the chance is a fractional 'p' for an occurance in one instance, it's (1-p) that it ''didn't'' occur thus (1-p)n that it didn't occur in any of 'n' instances and 1-(1-p)n that it did (at least once, possible several times or even all). Not so simple, but for p tending to zero it 'does' converge on 1.5 times for across three what you'd expect for two (albeit because 0*1.5=0). Like they say, "Lies, Damn Lies...", etc. ;) [[Special:Contributions/178.104.103.140|178.104.103.140]] 14:22, 16 August 2013 (UTC)

I don't think Randall is being attacked by a dog at all. What he's saying is that if you are going to think getting attacked by a shark is so likely, then you better be watching out for that never-gonna-happen dog scenario too. [[User:Jillysky|Jillysky]] ([[User talk:Jillysky|talk]]) 13:56, 16 August 2013 (UTC)

Is 0.000001% really "one in a million"?
;If 1% = 1 in 100, then
:0.1% = 1 in a 1,000
:0.01% = 1 in a 10,000
:0.001% = 1 in a 100,000
:0.0001% = 1 in a 1,000,000
:0.00001% = 1 in a 10,000,000
:'''0.000001% = 1 in a 100,000,000'''
Would it be more accurate to leave off the % sign?
Assuming I'm right, I think it'd be less confusing to leave it and reduce the numbers by a couple orders of magnitude.
--Clayton [[Special:Contributions/12.202.74.87|12.202.74.87]] 14:36, 16 August 2013 (UTC)

''If the chance of the dog attack is 0.000000001% (one in a billion) on each visit to the beach, then the chance of attack over two visits is 0.000000002% whereas in three visits it becomes 0.000000003%''

Um, no. Following that logic, if I go to the beach a billion times then I '''will''' get shot by a dog that is packing. Rather, each visit to the beach has it's own odds, like the rolling of dice? On any particular visit there's a one-in-a-billion chance. And that's true on each subsequent visit as well. Tuesday's visit to the beach isn't twice as dangerous just because I was at the beach on Monday. [[User:CFoxx|CFoxx]] ([[User talk:CFoxx|talk]]) 16:26, 16 August 2013 (UTC)
:For each visit that is the case. Because it's one visit, that's true. However, if (time not being a factor) one were to have a billion visits planned, the odds over all would be increased. Pretty sure that overall this means that you got the joke faster than I did. Thanks for the clarification! [[User:Theo|Theo]] ([[User talk:Theo|talk]]) 17:06, 16 August 2013 (UTC)
::The odds overall may increase with multiple visits. But not, at least, at the rate listed. Otherwise that billionth trip (if one survived that long as one is likely to do) would be certain death. [[User:CFoxx|CFoxx]] ([[User talk:CFoxx|talk]]) 17:30, 16 August 2013 (UTC)
:::Correct. Technically, the odds we are worried about are the "probability of being shot one or more times by a dog". So if the probability is 1/10^9 for any given day, than the odds of not being shot are (10^9-1)/10^9 for any given day, and the odds of not being shot over three days are (10^9-1)^3/10^27, and then the odds of being shot one or more times are 1-((10^9-1)^3/10^27), which is roughly 2.999999997000000001/10^9. That is close, but slightly less, than 3/10^9. [[Special:Contributions/206.174.12.203|206.174.12.203]] 18:01, 16 August 2013 (UTC)Toby Ovod-Everett
::::Absolute incorrect: You always have to look at the single event. More events do not belong together, you always have the same probability at each single event. So, even 10 billion events may or may NOT result in a disaster. Math isn't easy.--[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 19:17, 16 August 2013 (UTC)
:::::I believe what CFoxx was saying is that if the odds of something happening on any given day are one in three, then the odds of that thing happening at least once during a four day period is NOT 4/3rds! I was pointing out that the proper way to calculate the odds for a four day period is to say that the odds of it not happening on any given day are two in three. You take that probability and raise it to the fourth power, giving the odds that it won't happen at all during a four day period of 16/81, thus the odds that it will happen during that four day period is 65/81. I then did that same calculation for the 1 in a billion chance per day and applied it to the three day period, and recognized that he was correct that the true probability of the event happening one or more times over a three day period was not three times the probability of it happening on any given day, but also noted that the difference for a 1 in a billion chance over a small period is pretty close to the simplistic (but incorrect) approach. My rough estimate for the "one in a billion per day" event happening one or more times during a billion day period is 63.21%.[[Special:Contributions/206.174.12.203|206.174.12.203]] 21:33, 16 August 2013 (UTC)Toby Ovod-Everett
::::::Wow, we still have many great scientists here!--[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 21:46, 16 August 2013 (UTC)
::::::THANK YOU, Toby! [[User:CFoxx|CFoxx]] ([[User talk:CFoxx|talk]]) 18:09, 17 August 2013 (UTC)

Just a thought: is the title text a reference to the Sorites paradox? --AJ [[Special:Contributions/80.42.221.105|80.42.221.105]] 17:25, 16 August 2013 (UTC)

Rats! I made the newbie mistake of editing something before I found the discussion page. I looked for it, honest I did! I see that UTC has already brought up what I referred to as "Cueball's error" in my (pre-log-in) edit. I did find it hard to believe I'd be the first xkcd fan to notice this error. I think this is worth addressing in the explanation, though I of course won't take offense if someone wants to obliterate my edit and start over. (CLSI){{unsigned|CLSI}}

Maybe he means this: Florida man shot by his dog, police say http://usnews.nbcnews.com/_news/2013/02/26/17107343-florida-man-shot-by-his-dog-police-say?lite{{unsigned|Jb}}

Saying that unfortunately Cueball is mistaken in his calculations because he said 50% instead of 49.99999992% is a bit of an exaggeration. [[User:Xhfz|Xhfz]] ([[User talk:Xhfz|talk]]) 20:19, 16 August 2013 (UTC)

;Chaos at explain section
Please stop adding this, it does not explain the comic, it only belongs to this discussion page:

:Note that the 50% figure is an approximation. Assuming the odds of being attacked by a dog is ''x'', the odds of being attacked by a dog at least once in two visits is 1 - (1-''x'')2. The odds of being attacked at least once in three visits is 1 - (1-''x'')3. Therefore, if one visit has one in a billion probability of attack, then two visits have not 2 in a billion, but 1.999999999 in a billion. Similarly, three visits have a probability of 2.999999997 in a billion. Saying 50% instead of 49.99999992% is a reasonable approximation.

:Unfortunately, [[Cueball]] is mistaken in his calculations. This is easier to see with an event that has greater probability, such as a coin toss. Assuming the odds of getting heads in one flip is .5, the odds of getting heads at least once in two flips is .75 (i.e., 1 minus [.5 X .5], the odds of getting tails both times), and the odds of getting heads at least once in three flips is .875 (1 minus [.5 X .5 X .5], the odds of getting three tails in a row). Getting heads in three flips is not 50% more likely than getting heads in two flips. With very low probabilities (such as the probability of attack by a dog swimming with a handgun), Cueball's calculation gives an extremely close approximation of the actual probability, but one can't apply the same logic to events of just any probability.

::Cueball says *statistically* the risk of some bizarre event increases 50%. This is essentially correct as many have pointed out that 49.99999999 is not really statistically different than 50. What is likely bothering a lot of people (including myself) is that the explainxkcd description states "If the chance of the dog attack is one per billion on each visit to the beach, then the chance of attack over two visits *is* two per billion whereas in three visits it *becomes* three per billion." There are no weasel words like "approximately", "about", "around", etc. This reminds people of flatly incorrect uses of probabilities like the one you describe. But surely the probability of getting heads from a fair coin toss is not on a similar order of magnitude as the probability that a swimming dog shoots someone with a handgun. [[User:S|S]] ([[User talk:S|talk]]) 00:40, 17 August 2013 (UTC)

I had to think of http://xkcd.com/1102/ when reading the first paragraph of the explainxkcd description. (The context is different, but the dubious use of percentages is the same.) [[User:S|S]] ([[User talk:S|talk]]) 00:40, 17 August 2013 (UTC)

1252: Increased Risk

2013-08-17T18:08:54Z

CFoxx: /* Explanation */

{{comic
| number = 1252
| date = August 16, 2013
| title = Increased Risk
| image = increased_risk.png
| titletext = You may point out that strictly speaking, you can use that statement to prove that all risks are tiny--to which I reply HOLY SHIT WATCH OUT FOR THAT DOG!
}}

==Explanation==
{{incomplete}}
The panel satirises the common misunderstanding of the concept of percentage. Quoting a percentage figure, without mentioning the base which this ratio acts on is meaningless (outside of arithmetic for arithmetic's sake). Most everyday communication however, succumbs to such incompleteness. In the aftermath of this ambiguity, people tend to conflate relative and absolute changes.

If the probability of a shark attack at the North beach is one per million, then the probability of shark attack at the South beach is still not more than 1.2 per million. The difference between these values is not enough to normally justify choosing one beach over the other, even though a "20% greater" chance sounds significant when stated out of this larger context.

[[Cueball]] parodies the concern by noting that going to a beach three times instead of two their chances of attack by dogs with handguns in their mouths (a ludicrous and unrealistic scenario) increases by 50%. If the chance of the dog attack is one per billion on each visit to the beach, then the chance of attack increases over multiple visits. (It's still one in a billion for any specific visit.) This does not change the overall improbability of there ever being a dog swimming with a gun in its mouth.

[[Beret Guy]] misunderstands Cueball's probability, exhibiting the {{w|Gambler's fallacy}} by believing that, since they haven't been attacked in their first two trips, the chance of attack by dogs with handguns is higher on their third outing.

This is a common misunderstanding on statistics: While the overall probability of attack in three trips would be three times higher, it doesn't change the fact that in each individual trip, the probability is still the same; if they managed to avoid being attacked in their first two trips, these trips no longer factor into the probability equation of the third trip.

This also can be illustrated by coin flips: If one flips a coin 10 times in a row, no matter the result of each previous flip is, the odds of getting heads on the next coin flip remains 50%. In other words, past experience does not impact subsequent flips.

The title text discusses the argument that, if a tiny risk increased by 50% is still tiny, like this formulation of the {{w|paradox of the heap}}.

==Transcript==
:Ponytail: We should go to the north beach. Someone said the south beach has a 20% higher risk of shark attacks.
:Cueball: Yeah, but statistically, taking three beach trips instead of two increases our odds of getting shot by a swimming dog carrying a handgun in its mouth by '''''50%!'''''
:Beret Guy: Oh no! This is our third trip!
:Reminder: A 50% increase in a tiny risk is ''still tiny''.

{{comic discussion}}
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Beret Guy]]
[[Category:Math]]

1252: Increased Risk

2013-08-17T18:08:33Z

CFoxx: /* Explanation */

{{comic
| number = 1252
| date = August 16, 2013
| title = Increased Risk
| image = increased_risk.png
| titletext = You may point out that strictly speaking, you can use that statement to prove that all risks are tiny--to which I reply HOLY SHIT WATCH OUT FOR THAT DOG!
}}

==Explanation==
{{incomplete}}
The panel satirises the common misunderstanding of the concept of percentage. Quoting a percentage figure, without mentioning the base which this ratio acts on is meaningless (outside of arithmetic for arithmetic's sake). Most everyday communication however, succumbs to such incompleteness. In the aftermath of this ambiguity, people tend to conflate relative and absolute changes.

If the probability of a shark attack at the North beach is one per million, then the probability of shark attack at the South beach is still not more than 1.2 per million. The difference between these values is not enough to normally justify choosing one beach over the other, even though a "20% greater" chance sounds significant when stated out of this larger context.

[[Cueball]] parodies the concern by noting that going to a beach three times instead of two their chances of attack by dogs with handguns in their mouths (a ludicrous and unrealistic scenario) increases by 50%. If the chance of the dog attack is one per billion on each visit to the beach, then the chance of attack increases over multiple visits. (It's still one in a billion for any individual visit.) This does not change the overall improbability of there ever being a dog swimming with a gun in its mouth.

[[Beret Guy]] misunderstands Cueball's probability, exhibiting the {{w|Gambler's fallacy}} by believing that, since they haven't been attacked in their first two trips, the chance of attack by dogs with handguns is higher on their third outing.

This is a common misunderstanding on statistics: While the overall probability of attack in three trips would be three times higher, it doesn't change the fact that in each individual trip, the probability is still the same; if they managed to avoid being attacked in their first two trips, these trips no longer factor into the probability equation of the third trip.

This also can be illustrated by coin flips: If one flips a coin 10 times in a row, no matter the result of each previous flip is, the odds of getting heads on the next coin flip remains 50%. In other words, past experience does not impact subsequent flips.

The title text discusses the argument that, if a tiny risk increased by 50% is still tiny, like this formulation of the {{w|paradox of the heap}}.

==Transcript==
:Ponytail: We should go to the north beach. Someone said the south beach has a 20% higher risk of shark attacks.
:Cueball: Yeah, but statistically, taking three beach trips instead of two increases our odds of getting shot by a swimming dog carrying a handgun in its mouth by '''''50%!'''''
:Beret Guy: Oh no! This is our third trip!
:Reminder: A 50% increase in a tiny risk is ''still tiny''.

{{comic discussion}}
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Beret Guy]]
[[Category:Math]]

Talk:1252: Increased Risk

2013-08-17T18:05:14Z

CFoxx:

I think this is to address the old chestnut of "<something> will ''double'' your risk of getting cancer!", or the like, where the risk of getting that cancer (in this example) is maybe 1 in 10,000, so doubling the risk across a population wouldmake that a 1 in 5,000 risk to your health... which you may still consider to be an acceptable gamble if it's something nice (like cheese!) that's apaprently to blame and you'd find abstinence from it gives a barely marginal benefit for a far greater loss of life enjoyment. Also, this sort of figure almost always applies towards a ''specific form'' of cancer, or whatever risk is being discussed, meaning you aren't vastly changing your life expectancy at all. In fact, the likes of opposing "red wine is good/bad for you" studies can be mutually true by this same principle (gain a little risk of one condition, lose a little risk from another). (Note: I don't know of any particular "cheese gives you cancer!" stories doing the rounds, at the moment. I bet they have done, but I only mention it because I actually quite like cheese. And I probably ''wouldn't'' give it up under the above conditions.)

It's also possible that this covers the likes of "<foo> in <country> is 10 times more dangerous than it is <other country>" statements. Perhaps ''only'' ten incidents happened in the former, and a single instance in the latter, out the ''whole'' of each respective country. Or a single incident occured in both, but the second country is ten times the size, so gets 'adjusted for population' in the tables. And, besides which, that was just for one year and was just a statistical blip that will probably revert-towards-the-mean next year.

Finally, for a given risk of some incident happening on the first two trips, with no 'memory' or build-up involved, it pretty much is half-as-likely-again for the incident to have happened (some time!) in three separate trips. (Not quite, if those that lose against the odds and get caught by the incident the first or second trip never get to ''have'' a (second or) third trip... but for negligable odds like thegiven example, of the dog with the handgun, it's near-as-damnit so.) [[Special:Contributions/178.104.103.140|178.104.103.140]] 11:12, 16 August 2013 (UTC)

Where did "dogs with shotguns" come from? I only saw "handgun" in the comic. Besides, I interpreted the risk as being hit by a negligent discharge from the handgun, not being deliberately attacked by the dog. Also, since probabilities are the set of real numbers between 0 and 1 inclusive, there are an uncountable number of them. "A x% increase in a tiny risk is still tiny" is an inductive statement, which means it could only be used to argue that a countable set of numbers is tiny. [[Special:Contributions/76.64.65.200|76.64.65.200]] 12:24, 16 August 2013 (UTC)

:If induction base is uncountable, you can prove it for the whole [0; 1]. For example your induction base may be "every risk under 0.00000000000000000001% is tiny". --[[User:DiEvAl|DiEvAl]] ([[User talk:DiEvAl|talk]]) 12:38, 16 August 2013 (UTC)

I think it's worth mentioning that this comic doesn't [[985|distinguish between percentages and percentage points]]. --[[User:DiEvAl|DiEvAl]] ([[User talk:DiEvAl|talk]]) 12:35, 16 August 2013 (UTC)

Is it the case that doing something three times increases risk by 50% over two times inherently? I feel like this is the case, but it's early, here. Also, I'm not sure Randall is attacked by a dog, he may be using it as a diversion. I think that he's done this before. [[User:Theo|Theo]] ([[User talk:Theo|talk]]) 12:56, 16 August 2013 (UTC)
:(First, good point, DiEvAl, about the percentages/percentage-points. I ''knew'' I'd missed something out in my first thoughts. I actually tend to assume ''against'' percentage points, which is somewhat the opposite from what I've seen in the general public.)
:Actually, depends on how you count it. But I was using the "encounter 'n' incidents per trip", "encounter '2n' incidents per two trips", "encoutner '3n' incidents per three trips" measure, where 3n==2n+50%. But that works best with a baseline of >>1 incidents per trip assumed. In reality, if the chance is a fractional 'p' for an occurance in one instance, it's (1-p) that it ''didn't'' occur thus (1-p)n that it didn't occur in any of 'n' instances and 1-(1-p)n that it did (at least once, possible several times or even all). Not so simple, but for p tending to zero it 'does' converge on 1.5 times for across three what you'd expect for two (albeit because 0*1.5=0). Like they say, "Lies, Damn Lies...", etc. ;) [[Special:Contributions/178.104.103.140|178.104.103.140]] 14:22, 16 August 2013 (UTC)

I don't think Randall is being attacked by a dog at all. What he's saying is that if you are going to think getting attacked by a shark is so likely, then you better be watching out for that never-gonna-happen dog scenario too. [[User:Jillysky|Jillysky]] ([[User talk:Jillysky|talk]]) 13:56, 16 August 2013 (UTC)

Is 0.000001% really "one in a million"?
;If 1% = 1 in 100, then
:0.1% = 1 in a 1,000
:0.01% = 1 in a 10,000
:0.001% = 1 in a 100,000
:0.0001% = 1 in a 1,000,000
:0.00001% = 1 in a 10,000,000
:'''0.000001% = 1 in a 100,000,000'''
Would it be more accurate to leave off the % sign?
Assuming I'm right, I think it'd be less confusing to leave it and reduce the numbers by a couple orders of magnitude.
--Clayton [[Special:Contributions/12.202.74.87|12.202.74.87]] 14:36, 16 August 2013 (UTC)

''If the chance of the dog attack is 0.000000001% (one in a billion) on each visit to the beach, then the chance of attack over two visits is 0.000000002% whereas in three visits it becomes 0.000000003%''

Um, no. Following that logic, if I go to the beach a billion times then I '''will''' get shot by a dog that is packing. Rather, each visit to the beach has it's own odds, like the rolling of dice? On any particular visit there's a one-in-a-billion chance. And that's true on each subsequent visit as well. Tuesday's visit to the beach isn't twice as dangerous just because I was at the beach on Monday. [[User:CFoxx|CFoxx]] ([[User talk:CFoxx|talk]]) 16:26, 16 August 2013 (UTC)
:For each visit that is the case. Because it's one visit, that's true. However, if (time not being a factor) one were to have a billion visits planned, the odds over all would be increased. Pretty sure that overall this means that you got the joke faster than I did. Thanks for the clarification! [[User:Theo|Theo]] ([[User talk:Theo|talk]]) 17:06, 16 August 2013 (UTC)
::The odds overall may increase with multiple visits. But not, at least, at the rate listed. Otherwise that billionth trip (if one survived that long as one is likely to do) would be certain death. [[User:CFoxx|CFoxx]] ([[User talk:CFoxx|talk]]) 17:30, 16 August 2013 (UTC)
:::Correct. Technically, the odds we are worried about are the "probability of being shot one or more times by a dog". So if the probability is 1/10^9 for any given day, than the odds of not being shot are (10^9-1)/10^9 for any given day, and the odds of not being shot over three days are (10^9-1)^3/10^27, and then the odds of being shot one or more times are 1-((10^9-1)^3/10^27), which is roughly 2.999999997000000001/10^9. That is close, but slightly less, than 3/10^9. [[Special:Contributions/206.174.12.203|206.174.12.203]] 18:01, 16 August 2013 (UTC)Toby Ovod-Everett
::::Absolute incorrect: You always have to look at the single event. More events do not belong together, you always have the same probability at each single event. So, even 10 billion events may or may NOT result in a disaster. Math isn't easy.--[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 19:17, 16 August 2013 (UTC)
:::::I believe what CFoxx was saying is that if the odds of something happening on any given day are one in three, then the odds of that thing happening at least once during a four day period is NOT 4/3rds! I was pointing out that the proper way to calculate the odds for a four day period is to say that the odds of it not happening on any given day are two in three. You take that probability and raise it to the fourth power, giving the odds that it won't happen at all during a four day period of 16/81, thus the odds that it will happen during that four day period is 65/81. I then did that same calculation for the 1 in a billion chance per day and applied it to the three day period, and recognized that he was correct that the true probability of the event happening one or more times over a three day period was not three times the probability of it happening on any given day, but also noted that the difference for a 1 in a billion chance over a small period is pretty close to the simplistic (but incorrect) approach. My rough estimate for the "one in a billion per day" event happening one or more times during a billion day period is 63.21%.[[Special:Contributions/206.174.12.203|206.174.12.203]] 21:33, 16 August 2013 (UTC)Toby Ovod-Everett
::::::Wow, we still have many great scientists here!--[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 21:46, 16 August 2013 (UTC)
::::::THANK YOU, Toby!

Just a thought: is the title text a reference to the Sorites paradox? --AJ [[Special:Contributions/80.42.221.105|80.42.221.105]] 17:25, 16 August 2013 (UTC)

Rats! I made the newbie mistake of editing something before I found the discussion page. I looked for it, honest I did! I see that UTC has already brought up what I referred to as "Cueball's error" in my (pre-log-in) edit. I did find it hard to believe I'd be the first xkcd fan to notice this error. I think this is worth addressing in the explanation, though I of course won't take offense if someone wants to obliterate my edit and start over. (CLSI){{unsigned|CLSI}}

Maybe he means this: Florida man shot by his dog, police say http://usnews.nbcnews.com/_news/2013/02/26/17107343-florida-man-shot-by-his-dog-police-say?lite{{unsigned|Jb}}

Saying that unfortunately Cueball is mistaken in his calculations because he said 50% instead of 49.99999992% is a bit of an exaggeration. [[User:Xhfz|Xhfz]] ([[User talk:Xhfz|talk]]) 20:19, 16 August 2013 (UTC)

;Chaos at explain section
Please stop adding this, it does not explain the comic, it only belongs to this discussion page:

:Note that the 50% figure is an approximation. Assuming the odds of being attacked by a dog is ''x'', the odds of being attacked by a dog at least once in two visits is 1 - (1-''x'')2. The odds of being attacked at least once in three visits is 1 - (1-''x'')3. Therefore, if one visit has one in a billion probability of attack, then two visits have not 2 in a billion, but 1.999999999 in a billion. Similarly, three visits have a probability of 2.999999997 in a billion. Saying 50% instead of 49.99999992% is a reasonable approximation.

:Unfortunately, [[Cueball]] is mistaken in his calculations. This is easier to see with an event that has greater probability, such as a coin toss. Assuming the odds of getting heads in one flip is .5, the odds of getting heads at least once in two flips is .75 (i.e., 1 minus [.5 X .5], the odds of getting tails both times), and the odds of getting heads at least once in three flips is .875 (1 minus [.5 X .5 X .5], the odds of getting three tails in a row). Getting heads in three flips is not 50% more likely than getting heads in two flips. With very low probabilities (such as the probability of attack by a dog swimming with a handgun), Cueball's calculation gives an extremely close approximation of the actual probability, but one can't apply the same logic to events of just any probability.

::Cueball says *statistically* the risk of some bizarre event increases 50%. This is essentially correct as many have pointed out that 49.99999999 is not really statistically different than 50. What is likely bothering a lot of people (including myself) is that the explainxkcd description states "If the chance of the dog attack is one per billion on each visit to the beach, then the chance of attack over two visits *is* two per billion whereas in three visits it *becomes* three per billion." There are no weasel words like "approximately", "about", "around", etc. This reminds people of flatly incorrect uses of probabilities like the one you describe. But surely the probability of getting heads from a fair coin toss is not on a similar order of magnitude as the probability that a swimming dog shoots someone with a handgun. [[User:S|S]] ([[User talk:S|talk]]) 00:40, 17 August 2013 (UTC)

I had to think of http://xkcd.com/1102/ when reading the first paragraph of the explainxkcd description. (The context is different, but the dubious use of percentages is the same.) [[User:S|S]] ([[User talk:S|talk]]) 00:40, 17 August 2013 (UTC)

Talk:1252: Increased Risk

2013-08-16T17:30:00Z

CFoxx: not 100%

Talk:1252: Increased Risk

2013-08-16T16:26:40Z

CFoxx: Ummm, no. But thanks for playing.

1249: Meteor Showers

2013-08-09T16:11:13Z

CFoxx: sometimes the subject misunderstands journalists??

{{comic
| number = 1249
| date = August 9, 2013
| title = Meteor Showers
| image = meteor showers.png
| titletext = Remember, meteors always hit the tallest object around.
}}

This comic spoofs the way that astronomical events are often reported in the mass media — events are often tagged with undeserved superlatives or described as being more dramatic than they actually are. In some cases, outright misinformation is spread. This phenomenon occurs in part the result of over-eager scientists, and in part because of journalists misunderstanding the subject.

Meteor showers, for example, typically occur regularly each year. Sometimes meteor showers are in fact likely to be relatively spectacular - for example when the peak of the shower occurs when your part of the world is in darkness and there is little moonlight. However, even in these cases it must be understood that there is nothing unusual about the meteor shower itself.

Most of the meteor showers listed in the comic are real. These are the {{w|Quadrantids}}, [http://meteorshowersonline.com/showers/alpha-beta_centaurids.html Centaurids], {{w|Lyrids}}, Daytime Zeta Perseids, {{w|June Bootids|June Boötids}}, {{w|Southern Delta Aquariids}}, {{w|Perseids}}, {{w|Draconids}}, {{w|Orionids}}, {{w|Leonids}}, and {{w|Geminids}}.

Some of the showers are made up (see below).

*Quadrantids - January 4th - Bring pets inside during peak activity
*Tricuspids - January 21st - Not viewable in region 2 countries
:Made up. Apparently a play on the {{w|tricuspid valve}} in mammalian hearts, or possibly on bicuspid teeth. The mention of "Region 2" is a reference to {{w|region locking}}, a digital rights management (DRM) scheme intended to restrict media to certain areas. DRM of course does not apply to natural events. But ironically, meteor showers are also geographically restricted, and the visible area might roughly coincide with a DRM region. Further irony is that "Region 2" is actually Europe, Middle East, Egypt, Japan, South Africa, Swaziland, Lesotho, Greenland, French Overseas departments and territories, meaning that it's not strictly geographical.
*Centaurids - February 6th - Too faint to see without going outside
:Since most houses have opaque roofs, it would take a ''very'' bright meteor to be visible without going outside.
*Beta Aquariids - February 10th - Inverted shower converges toward Aquarius instead of radiating away
*Chelyabids - February 15th - Only one meteor per shower, but it's big.
:Made up. A reference to the February 15, 2013, {{w|Chelyabinsk meteor}} whose explosion shattered windows within a large radius.
*Lyrids - April 22nd - Meteors sometimes scream
*Daytime Zeta Perseids - June 9th - Likely a NASA hoax
*June Boötids - June 27th - 50/50 mix of meteors and shooting stars
:The "50/50 mix of meteors and shooting stars" is a joke, as "meteor" and "shooting star" are synonymous.
*Southern Delta Aquariids - July 19th - Meteors very bright, but stationary
*Dromaeosaurids - July 22th - Fast, highly intelligent, can open doors
:Made up. Dromaeosaurids are dinosaurs belonging to {{w|Dromaeosauridae}}, the family containing the genus ''Velociraptor'', well-known from the movie Jurassic Park, and a [[:Category:Velociraptors|popular xkcd-theme]]. When the comic was originally published, the date listed for this shower was June 12th. The main events of Jurassic Park take place on June 11th and 12th.
*Perseids - August 12th - Instead of falling from sky, meteors erupt from ground
*Tau Pyramids - August 15th - Visible even when eyes are closed
:Probably a reference to pyramidal cells, a type of neuron in the brain that is linked to cognition, and to the Tau particle, a heavy sibling of the electron. When they traveled outside of Earth's magnetosphere on their way to the Moon, Apollo astronauts saw flashes of light about every three minutes even with their eyes closed; these were caused by high energy particles (cosmic rays) penetrating their eyes and brain.
*Draconids - October 8th - Very slow, but follow you if you run
*Orionids - October 21st - Entire shower happens at once
*Leonids - November 17th - In 1966, unusually active Leonid shower killed God
:There ''was'' a very active Leonid shower. However, it occurred several months after the article "Is God Dead?" published in ''Time Magazine'' that year.
*Geminids - December 13th - Can be deflected with tennis rackets

The title text refers to the folk wisdom that ''lightning'' strikes the tallest thing around. [[Randall]] expressed frustration over how "maddeningly inexact" that statement is, and elaborated on the problem mathematically, on his [[what if?]]-blog, in the [http://what-if.xkcd.com/16/ post on lightning].

==Transcript==
:The xkcd guide to meteor showers
[There is a three-column table]
:; Name - Peak - Notes
:Quadrantids - January 4th - Bring pets inside during peak activity
:Tricuspids - January 21st - Not viewable in region 2 countries
:Centaurids - February 6th - Too faint to see without going outside
:Beta Aquariids - February 10th - Inverted shower converges toward Aquarius instead of radiating away
:Chelyabids - February 15th - Only one meteor per shower, but it's big.
:Lyrids - April 22nd - Meteors sometimes scream
:Daytime Zeta Perseids - June 9th - Likely a NASA hoax
:June Boötids - June 27th - 50/50 mix of meteors and shooting stars
:Southern Delta Aquariids - July 19th - Meteors very bright, but stationary
:Dromaeosaurids - July 22th - Fast, highly intelligent, can open doors
:Perseids - August 12th - Instead of falling from sky, meteors erupt from ground
:Tau Pyramids - August 15th - Visible even when eyes are closed
:Draconids - October 8th - Very slow, but follow you if you run
:Orionids - October 21st - Entire shower happens at once
:Leonids - November 17th - In 1966, unusually active Leonid shower killed God
:Geminids - December 13th - Can be deflected with tennis rackets

{{comic discussion}}
[[Category:Charts]]

663: Sagan-Man

2013-08-08T15:51:58Z

CFoxx: /* Explanation */ corrected spelling

{{comic
| number = 663
| date = November 16, 2009
| title = Sagan-Man
| image = sagan-man.png
| titletext = They laugh now, but within 10 years the city's entire criminal class will have quit to work on space research.
}}

==Explanation==
{{w|Carl Sagan}} was an advocate for science, space and {{w|SETI}} (Search for Extra-Terrestrial Intelligence). He wrote the book, Contact, which was later made into the movie by the same name. While Sagan did not emit anomalous radiation in his lifetime, he did receive acclaim for using radiation to synthesize amino acids from simpler chemicals.

This comic is parodying {{w|Spider-Man}}, in which Peter Parker is bitten by a radioactive spider to become Spider-Man. In this comic "a radioactive Carl Sagan" turns the person into "Sagan-Man". Apparently, Sagan-Man is able to stop thieves in their tracks by blowing their minds with scientific facts.

==Transcript==
:[Bitten by a radioactive Carl Sagan in 1995, Sagan-Man possesses the powers and abilities of Carl Sagan.]
:Victim, off-panel: Help! Thief!
:[Sagan-Man spins around. A blue cape appears on his back.]
:[Sagan-Man runs towards the direction of the shout.]
:[He encounters the thief, holding a purse.]
:Sagan-Man: Hey, you!
:Thief: What?
:Sagan-Man: Do you realize just how crazy it is that we’ve ''BEEN TO THE MOON?''

{{comic discussion}}
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring real people]]
[[Category:Comics with color]]
[[Category:Astronomy]]

Talk:1248: Sphere

2013-08-08T15:50:06Z

CFoxx: responding

More specifically,a geoid.--[[User:Guru-45|Guru-45]] ([[User talk:Guru-45|talk]]) 08:51, 7 August 2013 (UTC)
:Astronomers observe objects in the sky, not the Earth.--[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 11:19, 7 August 2013 (UTC)
::Astronomers live on the surface of the Earth, not on the surface of the sky (celestial sphere). [[Special:Contributions/167.107.191.217|167.107.191.217]] 13:25, 7 August 2013 (UTC)

Are you sure “Sphere” refers to “hemisphere” and not simply to earth? After all, she’s trapped on earth and not on the celestial sphere. [[User:Quoti|Quoti]] ([[User talk:Quoti|talk]]) 11:24, 7 August 2013 (UTC)
:It's the hemisphere, see my comment above.--[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 11:46, 7 August 2013 (UTC)
:: I'm assuming you're referring to the "light-sphere" whose origin lies at the astronomer's location, and thus the universe always being bigger than the places he can physically visit. Still though, the statement "They can't travel to the places they observe" isn't accurate. We've been to the moon for instance. And then of course, there are always the unknown unknowns of the universe and interstellar travel. [[Special:Contributions/220.224.246.97|220.224.246.97]] 12:19, 7 August 2013 (UTC)
::: The fact that we, the human race, have been to the moon is no comfort to anyone who's seen the wonders revealed by the HST (which isn't even suitable for inspecting the moon). We are, indeed, "trapped" here on Earth, into the foreseeable future. ''— [[User:Tbc|tbc]] ([[User talk:Tbc|talk]]) 13:22, 7 August 2013 (UTC)''
: I read it as earth. It's a sphere and we're all trapped on its surface and astronomy classes make you aware of this fact more than your everyday experiences. Also, doesn't "hemisphere" mean "half sphere"? like northern and southern hemisphere of the earth? [[User:Peter|Peter]] ([[User talk:Peter|talk]]) 12:48, 7 August 2013 (UTC)

Do we maybe have a reference to [[1246]]? [[Special:Contributions/217.81.31.20|217.81.31.20]] 11:37, 7 August 2013 (UTC)
:That comic belongs more to space science than to astronomers.--[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 11:46, 7 August 2013 (UTC)

I'm sure the sphere is Earth. We don't live on the '''surface''' of the universe. Everybody in http://forums.xkcd.com/viewtopic.php?f=7&t=104172 agrees. [[Special:Contributions/167.107.191.217|167.107.191.217]] 13:12, 7 August 2013 (UTC)

"This totally occupies her mind, and she feels frustrated that she can only learn about those mind-boggling places, and not visit them herself." Wow. She must have been in a class? She's "totally" occupied? She's frustrated? (Not wistful, or resigned, or just aware of a fact mind you.) She isn't just thinking about the size of space, but apparently really, really wants to actually travel there. (To where, exactly? What "mind boggling" places? "Space"? Seems rather general.) You got all that deep and specific feeling from just her using the word "trapped"? Looks like reading a lot into things, to me. [[User:CFoxx|CFoxx]] ([[User talk:CFoxx|talk]]) 15:53, 7 August 2013 (UTC)
:I try to not to make the explanations too dry; they are and should often be interpretations to some extent. On the other hand yeah, you are probably right that I read too much emotion into it. I changed the things you commented on. –[[User:St.nerol|St.nerol]] ([[User talk:St.nerol|talk]]) 18:29, 7 August 2013 (UTC)
::"I try to not to make the explanations too dry" And your efforts are very much appreciated. Hat tip! [[User:CFoxx|CFoxx]] ([[User talk:CFoxx|talk]]) 15:50, 8 August 2013 (UTC)
:@CFoxx - Absolutely. In XKCD, there are no shades of grey. (really, look for yourself) [[User:JamesCurran|JamesCurran]] ([[User talk:JamesCurran|talk]]) 19:43, 7 August 2013 (UTC)
::Heh. :) [[User:CFoxx|CFoxx]] ([[User talk:CFoxx|talk]]) 15:50, 8 August 2013 (UTC)

Hey, what the hell are you doing? "The sphere she mentions..." is absolutely wrong, the word ''Sphere'' appears only at the title and the title text! Megan is just impressed by the vast size of the universe.--[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 16:21, 7 August 2013 (UTC)
:And to all you ''Earth'' theorists, tell me why Randall mentions astronomers and NOT the entire mankind? And that, after Megan talks about a big universe. Astronomers do not observe the Earth but objects in that big universe, which is from a viewpoint on Earth just a sphere.--[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 16:21, 7 August 2013 (UTC)
::One more: Astronomers are not trapped to the surface of the Earth because they use many space telescopes even beyond of earth's orbit. They are also using probes at many planets and more all over the solar system.--[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 17:02, 7 August 2013 (UTC)
:::Would you please look at the first panel … And just using space telescopes doesn’t mean you’re no longer trapped. Imagine yourself being trapped in a cage with a satellite dish to communicate with a space telescope (well … just imagine that). You’re not going anywhere by using that telescope. I think you confuse “being trapped” with “being limited”. Being trapped somewhere doesn’t mean your observation is limited to that place too. [[User:Quoti|Quoti]] ([[User talk:Quoti|talk]]) 17:54, 7 August 2013 (UTC)
::::Ok, I did ignore the first panel, sorry about that. But the Earth is a {{w|geoid}} and absolutely doesn't match the criteria for a {{w|sphere}}. So, like in democracy the mass does win, but I'm still sure I'm right.--[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 19:13, 7 August 2013 (UTC)
:She does mention a sphere, so I changed it back. No hard feelings (I hope). –[[User:St.nerol|St.nerol]] ([[User talk:St.nerol|talk]]) 18:29, 7 August 2013 (UTC)
::I don't mind, but it seems I'm the only astronomer and physicist here.--[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 19:13, 7 August 2013 (UTC)

After some more thoughts on this, why nobody (even myself) did raise the idea that Randall talks about both interpretations? Nevertheless, if the sphere is interpreted as the surface of the Earth there is a need to explain the geoid discrepancy to an ideal sphere, as mentioned in the very first post here.--[[User:Dgbrt|Dgbrt]] ([[User talk:Dgbrt|talk]]) 19:51, 7 August 2013 (UTC)
:I fixed a sentence on the discrepancy (with some Wikipedia help). Interesting stuff! I think that Megan answers Cueballs question quite literary. How are you? Trapped on a 2-dimensional surface. The 'celestial sphere'-thing seems too far fetched... –[[User:St.nerol|St.nerol]] ([[User talk:St.nerol|talk]]) 10:54, 8 August 2013 (UTC)

This "a sphere is a surface and has no surface" is too much nitpicking. Wikipedia (http://en.wikipedia.org/wiki/Sphere) talks about calculating the surface area of a sphere. I think "surface of sth" is not very rigorously defined. Often two dimensional manifolds are called surfaces, and a sphere is one, and the surface (different meaning) of the earth is roughly a sphere. What a sphere doesn't have is a border. [[User:Peter|Peter]] ([[User talk:Peter|talk]]) 11:54, 8 August 2013 (UTC)

The is trapped on the surface of this sphere, since you can walk on it forever, without ever leaving it[[User:Oscar|Oscar]] ([[User talk:Oscar|talk]]) 12:20, 8 August 2013 (UTC)

Talk:1248: Sphere

2013-08-07T15:54:20Z

CFoxx:

Talk:1248: Sphere

2013-08-07T15:53:20Z

CFoxx: A complaint about a stubbed toe isn't a deep contemplation of the history of medicine.

1247: The Mother of All Suspicious Files

2013-08-05T16:35:00Z

CFoxx: /* Explanation */ just one dialog

{{comic
| number = 1247
| date = August 5, 2013
| title = The Mother of All Suspicious Files
| image = the_mother_of_all_suspicious_files.png
| titletext = Better change the URL to 'https' before downloading.
}}

==Explanation==
The save dialogue shows a download from [http://www.utrace.de/?query=65.222.202.53 65.222.202.53] with a very long file title. Many of the extensions used inside there indicate executable code. You also see common download syntax for a pirated movie, {{w|Hackers (film)|Hackers}}, likely included to appear malicious to anyone skimming but is actually a movie about hackers, making it a benign reference rather than malicious. The ".LNK" extension is the windows extension for a shortcut (the extension is normally hidden to the user), whereas ".LNK.ZDA.GNN" extensions are references to Link, Zelda, and Ganon, important characters from the Legend of Zelda video game franchise.

The file seems to be an executable, but other file types referenced include:
* AUTOEXEC.BAT - which is automatically run during startup on Windows/DOS operating systems.
* MY%20OSX%20DOCUMENTS - referencing the OSX operating system (%20 is a representation of a space in a URL, i.e. it reads as "MY OSX DOCUMENTS").
* INSTALL.EXE - a typical installer
* RAR - a compressed archive file type
* INI - a settings file type
* TAR - a file archive popular in UNIX and UNIX-like operating systems
* DOÇX - looks like a Microsoft Word file type, but isn't
* PHPHPHP - a play on PHP files, a kind of server-based web page file type
* XHTML - another web page file type
* TML - stands for Transducer Markup Language, an XML based markup language that specifies how to capture, time-tag and describe sensor data
* XTL - another play on XHTML?
* TXXT - a play on TXT file types
* 0DAY - a reference to a {{w|zero-day exploit}}
* HACK.ERS_(1995)_BLURAY_CAM-XVID - a reference to the 1995 Hackers movie, but pirated movies would either be a BlurayRIP/DVDRIP or CAM, but not both at the same time unless you used a camera to recored the Blueray movie as it played?
* EXE - an executable file type
* [SCR] - a Windows screensaver (a popular way to get malware onto somebody's Windows machine)
* LISP - {{w|Lisp (programming language)|the programming language}}
* MSI - an installer file type
* WRBT OBJ - A reference to the line of code Dennis Nedry used in {{w|Jurassic Park (film)|Jurassic Park}} to shut down key systems
* O - The extension for a linker file, an intermediary created when compiling C code.
* H - The file extension of a header file in C code.
* SWF - Shockwave Flash file type
* DPKG - Debian package file type
* APP - an application on Mac OS X operating system
* ZIP - compressed archive file type
* CO.GZ - looks like a {{w|List_of_Internet_top-level_domains|top-level domain}} for an unknown country, but it is a compressed file using GNU zip.
* A.OUT - Default filename when creating an executable on Linux or other UNIX-like operating systems if none was specified for the compiler.

The title text suggests changing from http to https, as if encrypting a suspicious file before downloading it is somehow better than downloading it unencrypted. http (Hyper Text Transfer Protocol) and https (Hyper Text Transfer Protocol - Secure) are the two common protocols for getting web pages and web downloads. http is the simple download, whereas https adds an SSL encryption layer so the item being downloaded cannot be viewed unencrypted by anyone except the end recipient. Changing "http" to "https" is a common suggestion to improve security when browsing the web from an insecure network (such as a public wifi hotspot) to avoid surveillance or hijacking to a malicious website; Google automatically switches to https for all mail accounts and is starting to do so with searches. The end recipient will still get whatever nasties were in the original, however - encrypting it doesn't change the content at all.

The IP address referenced in the comic, 65.222.202.53, is currently being used by the shellcode of a Javascript 0-day exploit for the Tor Browser Bundle being run by the FBI to phone home over the clearnet and de-anonymize visitors to websites on Freedom Hosting that are serving child pornography. [http://www.reddit.com/r/onions/comments/1jmrta/founder_of_the_freedom_hosting_arrested_held/]

==Transcript==
:[A save dialogue popup with an alert sign.]
:Warning!
:This type of file can harm your computer! Are your sure you want to download: <nowiki>http://65.222.202.53/~TILDE/PUB/CIA-BIN/ETC/INIT.DLL?FILE=--AUTOEXEX.BAT.MY%20OSX%20DOCUMENTS-INSTANLL.EXE.RAR.INI.TAR.DOCX.PHPHPHP.XHTML.TML.XTL.TXXT.0DAY.HACK.ERS_(1995)_BLURAY-CAM_XVID.EXE.TAR.[SCR].LISTP.MSI.LNK.ZDA.GNN.WRBT.OBJ.O.SWF.DPKG.APP.ZIP.TAR.CO.GZ.OUT.EXE</nowiki>

:[Two buttons:]
:Cancel Save

{{comic discussion}}
[[Category:Comics with color]]
[[Category:Computers]]