https://www.explainxkcd.com/wiki/api.php?action=feedcontributions&user=86.148.194.183&feedformat=atomexplain xkcd - User contributions [en]2024-03-19T13:09:35ZUser contributionsMediaWiki 1.30.0https://www.explainxkcd.com/wiki/index.php?title=882:_Significant&diff=49947882: Significant2013-10-03T18:42:50Z<p>86.148.194.183: /* Explanation */</p>
<hr />
<div>{{comic<br />
| number = 882<br />
| date = April 6, 2011<br />
| title = Significant<br />
| image = significant.png<br />
| imagesize = <br />
| titletext = So, uh, we did the green study again and got no link. It was probably a-- "RESEARCH CONFLICTED ON GREEN JELLY BEAN/ACNE LINK; MORE STUDY RECOMMENDED!"<br />
}}<br />
<br />
==Explanation==<br />
This comic is about the often difficult relationship between science, statistics and the media. [[Megan]] and [[Cueball]] commission some research on the link between jelly beans and acne. At first the scientists do not want to stop playing the addictive game {{w|Minecraft}} (which has been referenced in a [[861|previous xkcd]]), but they do eventually start.<br />
<br />
First some basic statistical theory. Let's imagine you are trying to find out if jelly beans cause acne. To do this you could find a group of people and randomly split them into two groups - one group who you get to eat lots of jelly beans and a second group who are banned from eating jelly beans. After some time you compare whether the group that eat jelly beans have more acne than those who do not. If more people in the group that eat jelly beans have acne then you might think that jelly beans cause acne. However, there is a problem.<br />
<br />
Some people will suffer from acne whether they eat jelly beans or not and some will never have acne even if they do eat jelly beans. There is an element of chance in how many people prone to acne are in each group. What if, purely by chance, all the group we selected to eat jelly beans would have had acne anyway while those who didn't eat jelly beans were the lucky sort of people who never get spots? Then, even if jelly beans did not cause acne, we would conclude that jelly beans did cause acne. Of course it is very unlikely that all the acne prone people end up in one group by chance, especially if we have enough people in each group. However, to give more confidence in the result of this type of experiment, scientists use statistics to see how likely it is that the result they find is purely by chance. This is known as {{w|statistical hypothesis testing}}. Before we start the experiment, we choose a threshold known as the significance level. In the comic the scientists choose a threshold of 5%. If they find that that more of the people who ate jelly beans had acne and the chance it was a purely random result is less than 1 in 20, they will say that jelly beans do cause acne. If however, the chance that their result was purely by random chance is greater than 5% they will say they have found no evidence of a link. The important point is this - '''there could still be a 1 in 20 chance that this result was purely a statistical fluke'''.<br />
<br />
In the comic, the scientists find no link between jelly beans and acne (the probability that the result is by chance is more than 5% i.e. p > 0.05) but then Megan and Cueball ask them to see if only one colour of jelly beans is responsible. They test 20 different colors each at a significance level of 5%. If the probability that each trial gives a false positive result is 1 in 20, then by testing 20 different colors it is now highly likely that at least one jelly bean test will give a false positive. In this case they find that green jelly beans do cause acne. <br />
<br />
Also, for the study on green jelly beans, the scientists say they have carried it out to a level of significance of (P<0.05), meaning that there was a 95% chance the result was caused by chance (i.e. it occurred randomly) whereas for all the others it is (P>0.05) so there is only a 5% chance it was caused by chance. They were too lenient with their analysis of the results, and thus claimed the results were significant whe in fact they weren't, and green jelly beans do not cause acne. <br />
<br />
This leads to a big newspaper headline saying '''GREEN JELLY BEANS CAUSE ACNE''' but when the scientists {{w|Reproducibility|repeat the experiment}} (another key part of the scientific method) they find no evidence for a link. They try to tell the reporter that it was probably a coincidence but that is not news. Instead it leads to another major headline saying '''RESEARCH CONFLICTED'''.<br />
<br />
This can be an issue with more serious matters than jelly beans and acne - at any one time there are many studies about possible links between substances (e.g. red wine) and illness (e.g. cancer). Because only the positive results get reported, this limits the value any single study has - especially if the mechanism linking the two things is not known. For more information see: http://www.fallacyfiles.org/multcomp.html<br />
<br />
==Transcript==<br />
:[Ponytail runs up to another person, who subsequently points off-panel where there are presumably scientists.]<br />
:Ponytail: Jelly beans cause acne!<br />
:Another: Scientists! Investigate!<br />
:Scientists: But we're playing Minecraft! ...Fine.<br />
<br />
:[Two scientists. Cueball has safety goggles, Megan has a sheet of notes.]<br />
:Cueball: We found no link between jelly beans and acne (p > 0.05).<br />
:[Back to the original two.]<br />
:Another: That settles that.<br />
:Ponytail: I hear it's only a certain color that causes it.<br />
:Another: Scientists!<br />
:Scientists: But Miiiinecraft!<br />
<br />
:[20 near identical small panels follow, 4 rows 5 columns.]<br />
:Cueball: We found no link between purple jelly beans and acne (p > 0.05).<br />
:Cueball: We found no link between brown jelly beans and acne (p > 0.05).<br />
:Cueball: We found no link between pink jelly beans and acne (p > 0.05).<br />
:Cueball: We found no link between blue jelly beans and acne (p > 0.05).<br />
:Cueball: We found no link between teal jelly beans and acne (p > 0.05).<br />
:Cueball: We found no link between salmon jelly beans and acne (p > 0.05).<br />
:Cueball: We found no link between red jelly beans and acne (p > 0.05).<br />
:Cueball: We found no link between turquoise jelly beans and acne (p > 0.05).<br />
:Cueball: We found no link between magenta jelly beans and acne (p > 0.05).<br />
:Cueball: We found no link between yellow jelly beans and acne (p > 0.05).<br />
:Cueball: We found no link between grey jelly beans and acne (p > 0.05).<br />
:Cueball: We found no link between tan jelly beans and acne (p > 0.05).<br />
:Cueball: We found no link between cyan jelly beans and acne (p > 0.05).<br />
:Cueball: We found a link between green jelly beans and acne (p < 0.05).<br />
:Off-panel: ''WHOA!''<br />
:Cueball: We found no link between yellow jelly beans and acne (p > 0.05).<br />
:Cueball: We found no link between beige jelly beans and acne (p > 0.05).<br />
:Cueball: We found no link between lilac jelly beans and acne (p > 0.05).<br />
:Cueball: We found no link between black jelly beans and acne (p > 0.05).<br />
:Cueball: We found no link between peach jelly beans and acne (p > 0.05).<br />
:Cueball: We found no link between orange jelly beans and acne (p > 0.05).<br />
<br />
:[Newspaper front page.]<br />
:NEWS Green Jelly Beans Linked To Acne! 95% Confidence<br />
:[There is a picture of 3 green jelly beans.]<br />
:Only 5% chance of coincidence!<br />
:Scientists...<br />
<br />
{{comic discussion}}<br />
[[Category:Comics featuring Cueball]]<br />
[[Category:Comics featuring Megan]]<br />
[[Category:Comics featuring Ponytail]]<br />
[[Category:Math]]<br />
[[Category:Comics with color]]</div>86.148.194.183https://www.explainxkcd.com/wiki/index.php?title=451:_Impostor&diff=49678451: Impostor2013-09-28T20:38:25Z<p>86.148.194.183: /* Explanation */</p>
<hr />
<div>{{comic<br />
| number = 451<br />
| date = July 18, 2008<br />
| title = Impostor<br />
| image = impostor.png <br />
| titletext = If you think this is too hard on literary criticism, read the Wikipedia article on deconstruction.<br />
}}<br />
<br />
==Explanation==<br />
While the comic is ostensibly about grad students, it is really [[Randall]]'s way of poking fun at different fields. Given that engineers can detect his {{w|bullshit|BS}} quickly suggests he regards engineering with some respect. In other words, he thinks engineering has a low {{w|Bollocks#.22Talking_bollocks.22_and_.22Bollockspeak.22|BS quotient}}. Similarly with linguists. He clearly things less of sociology, since his BS can go undetected for considerably longer. And the field of "Literary Criticism" is something he consider mostly, or entirely, BS, since he claims his BS has repeatedly been published.<br />
<br />
The first panel shows [[Cueball]] discussing an engineering problem with [[Ponytail]]. {{w|logarithm|Logarithms}} are a mathematical tool used for expressing an exponential relationship as a linear one. While this has many uses in a variety of fields, it is not a suitable tool for dissipating excess heat. (It might have value in plotting temperature change over time, or temperature over distance, however.)<br />
<br />
Since {{w|Klingon language|Klingon}} is a constructed language designed to sound "alien" and which explicitly avoids sounding like any human language, it cannot be part of any real-world linguistic family. Any linguist who knows what a Klingon is would instantly recognize his statement as a joke, so the detection time should be only a few seconds. His assertion that his BS went undetected for over a minute suggests he does not expect linguists to be familiar with Star Trek.<br />
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The third panel is a bit more subtle. While {{w|sociology}} can certainly use ranking as an analytical tool, the trouble lies in the complete lack of meaning in the tags "best" and "worst". Detecting this as BS requires a bit more effort on the part of the sociology grad students.<br />
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Literary criticism, on the other hand, is almost completely written in {{w|buzzword|buzz words}} and {{w|jargon}}, and is thus difficult for anyone, including those versed in the field, to understand. His assertion that he published 8 papers and 2 books could also be his way of saying that he doesn't believe anyone actually reads any of the stuff published in the field.<br />
<br />
==Transcript==<br />
:My Hobby: Sitting down with grad students and timing how long it takes them to figure out that I'm not actually an expert in their field.<br />
<br />
:Engineering:<br />
:Student: Our big problem is heat dissipation<br />
:Cueball: Have you tried logarithms?<br />
:48 seconds<br />
<br />
:Linguistics:<br />
:Cueball: Ah, so does this Finno-ugric family include, say, Klingon?<br />
:63 Seconds<br />
<br />
:Sociology:<br />
:Cueball: Yeah, my latest work is on ranking people from best to worst.<br />
:4 Minutes<br />
<br />
:Literary Criticism:<br />
:Cueball: You see, the deconstruction is inextricable from not only the text, but also the self.<br />
:Eight papers and two books and they haven't caught on.<br />
<br />
{{comic discussion}}<br />
[[Category:Comics featuring Cueball]]<br />
[[Category:Comics featuring Megan]]<br />
[[Category:Comics featuring Ponytail]]<br />
[[Category:My Hobby]]</div>86.148.194.183