1999: Selection Effect

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"1999", this comic's number, redirects here. For the comic named "1999", see 855: 1999.
Selection Effect
fMRI testing showed that subjects who don't agree to participate are much more likely to escape from the machine mid-scan.
Title text: fMRI testing showed that subjects who don't agree to participate are much more likely to escape from the machine mid-scan.


The title refers to the effect in scientific fields where instead of investigating the whole population (i.e. all cancer patients or all trees) only a subset is analysed. This is common practice as the analysis of all specimens is often impractical. However, special care needs to be taken when selecting the sample to ensure that it accurately represents the general population. Otherwise the results are misleading and do not reflect reality. For example if 1000 people are asked about the numbers of cars they own but all live in a city the results cannot be generalised to the whole country. This is called the selection bias. If non-human subjects are studied this can be avoided by randomising the selection process, but this is not possible with humans as they cannot be forced to participate in a study against their will. For example, if people are asked to participate in a study about their political views it is likely that the responders care about politics while people with no clear opinion do not bother to respond. This is called the self-selection bias.

Ponytail says that people who agree to be in a study at their lab are less likely to attempt to escape. The only way Ponytail could have come to this conclusion is if she compared those people to people who did not agree to be in the study. This implies that Ponytail has recently kidnapped people for a study, and that most of the people she kidnapped called the police, as one should do when being kidnapped. This makes sense, since if you agreed to the study, you know why you are there, while if you didn't, you may have been kidnapped. As Ponytail presents this as a finding, it appears that she was attempting to establish a protocol for randomised selection of human subjects and comparing it to the normal selection process.

The comic shows Ponytail being allowed to present the results of this study at a conference; reputable scientific journals and conferences should not legitimize studies that clearly violate their ethical norms, such as by failing to obtain informed consent from human subjects before experimenting on them. Unfortunately, involuntary studies are published and presented, like this 2014 Facebook's emotional contagion study. It is not clear how many people who did agree to participate may have attempted to call the police for assistance regardless; compare the Stanford Prison Experiment. This is similar to previous comics where obvious things are presented in obfuscated, scientific ways (e.g. 1990: Driving Cars). Of course, any study of the way people behave when being kidnapped for scientific experiments would inherently involve kidnapping them. Therefore there is no way this kind of research could be done in an ethical fashion.

The title text refers to a technique that measures brain activity, called Functional magnetic resonance imaging (fMRI). Of course it's much more likely that people who did not sign up will resist and escape before the scan is complete. This technique has been mentionned before, such as in 1453: fMRI and 1526: Placebo Blocker


[Ponytail stands on a podium giving a presentation in front of a chart with some box plots.]
Ponytail: Our research shows that compared to the overall population, people who agree to participate in scientific studies are significantly less likely to call the police to rescue them from our lab.

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The selection effect is a bias in the results of a study because the study participants are not a random sample of the general population. For example, a study performed on college students may be biased toward better-educated people, or a study on social interaction may be affected by how many participants have the same first language as the investigators.

The Dining Logician (talk) 19:17, 28 May 2018 (UTC)

One more comic until we hit 2000! Which means on July 11th, the comic number will finally match up with the date (and will certainly be the only time ever). Like an eclipse! Some Commenter (talk) 12:23, 28 May 2018 (UTC)

Just 49 to go until a big round-number milestone! (and just 1 until a big round number kilometerstone) -- 21:54, 28 May 2018 (UTC)
Well, arguably only two more to go, as there was no comic for #404 (Found this out on accident a few minutes ago looking for something unrelated.) But that means the 1000th comic was the 999th too.Linker (talk) 12:47, 29 May 2018 (UTC)

There was no comic #404 because Randall intended the "Page Not Found" error as comic #404. The Dining Logician (talk) 20:18, 29 May 2018 (UTC)

As I recall Mr Munroe's 404th comic was something that he created to mess with us: I remember being surprised by it, looking at the source code of the page and deciding that it was not an error. SDT 02:25, 30 May 2018 (UTC) addendum: a /very/ good April fool's joke: Even if it wasn't (it was) he's still got me ;p SDT 02:39, 30 May 2018 (UTC)

I don't think escaping from MRI is that easy. There is reason why it's known to be problem for claustrophobic people. -- Hkmaly (talk) 22:46, 28 May 2018 (UTC)

It it not that it is hard to escape from an MRI, unless you are somehow restrained or disabled. It is just that it feels that way because your head is in a tunnel. 13:31, 29 May 2018 (UTC)
Is it dangerous to leave an MRI mid-scan? 18:57, 29 May 2018 (UTC)
No. Smurfix (talk) 20:42, 30 May 2018 (UTC)

It could be if your escape attempt brings something metallic into the MRI field. The Dining Logician (talk) 19:37, 29 May 2018 (UTC)

Should we mention trivia of comics using the same platform? https://xkcd.com/1781/ 16:58, 29 May 2018 (UTC)

https://xkcd.com/1453/ is a simliar, meta-research thing comic. There seems to be several of these now, perhaps a category or at least a mention should be appropriate? 08:03, 30 May 2018 (UTC)