And from explain xkcd:
This strip plays on certain experiments involving human subjects. Ponytail is questioning the reliability of Megan's experimental results, given that her human subjects appear to be extremely unusual and highly sociopathic.explain xkcd is so matter of fact.
In the second panel, she mentions that several people in one study had been arrested for arson. Megan begins to suggest that the arson is a side effect of whatever is being tested before she learns that the arsonists are in the control group – that is, the group that is not subjected to whatever is being tested and is used as a comparison to see the differences in the people who are actually being tested. This result is "troubling", as the control group would not be expected to have such a high rate of incidence of arsonists. The implication is that her subjects are not representative of the general population, but appear to have been selected from some aberrant subpopulation, such as a prison or mental institution. Or she could have recruited them through an announcement that catered in some way to arsonists. An alternate explanation comes from comic 790: Control, in which Randall notes his hobby of sneaking into experiments and giving LSD to the control groups. Yet another explanation could be that Ponytail went looking for some clusters of characteristics in the sample population, which had no connection to the study criteria, and happened upon the arson arrests - such clusters are expected if you look at enough different characteristics.
The third panel alludes to the prisoner's dilemma, in which two subjects must independently decide whether to "collaborate" with or "betray" the other subject based on different rewards for each choice (often framed as a different length of prison sentence, or a different amount of money). The rewards tier are selected so that the outcomes for each individual from best to worst are: betraying a collaborator, collaborating with a collaborator, betraying a betrayer, collaborating with a betrayer. The thought experiment is considered interesting as it's uncertain what the most logical course of action, as choosing betrayal always improves one's situation, yet being in identical situations with no knowledge of each other, it's also logical for both prisoners to make the same choice and both collaborating is better than both betraying. Of course, it would not be expected that normal people would simply betray each other for no reason, without benefiting from it in any way.
The last panel references the Milgram experiment, in which subjects were instructed by experimenters to administer electric shocks to an unseen third party. The unseen third party was part of the experiment and pretended to be in agony....MORE