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In Richard Feynman's classic Cargo Cult Science speech. He talks about a type of scientific error made, where a person takes a previous experimental result for granted when designing an experiment.

Other kinds of errors are more characteristic of poor science. When I was at Cornell, I often talked to the people in the psychology department. One of the students told me she wanted to do an experiment that went something like this — it had been found by others that under certain circumstances, X, rats did something, A. She was curious as to whether, if she changed the circumstances to Y, they would still do A. So her proposal was to do the experiment under circumstances Y and see if they still did A. I explained to her that it was necessary first to repeat in her laboratory the experiment of the other person — to do it under condition X to see if she could also get result A, and then change to Y and see if A changed. Then she would know the the real difference was the thing she thought she had under control.

I'm not sure I understand what sort of fallacy is being committed in this instance. What exactly is the problem?

Thanks.

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I'm not sure this is really a philosophical question, it's more a matter of scientific process.

However, the issue Feynman is talking about is controlling the variables in an experiment. If you do X and the rats do A, and I do Y and the rats do B, we don't know that X to Y is the cause of the change, because there are different rats, a different lab, a different scientist in charge, and probably any number of other variables we haven't considered. We need to make sure that we can observe the rats displaying the different behaviors where X to Y is the only change --that's why you have the control group that also participates in the experiment.

  • I would add simply that peer review is part of the scientific method. It is like depending on a legal law working a certain way after it's been signed by the President before it's been challenged in court. Peer review is the judicial branch of science. – Kevin Holmes Dec 11 '13 at 16:28
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    @KevinHolmes, this has nothing to do with peer review: one has to repeat X even if 1000 other labs have already confirmed the original research. This is about reproducing the experiment to establish a baseline for the change from X to Y, to make sure that nothing else is different in YOUR lab that could have affected the outcome, just as Chris explained. – Michael Dec 11 '13 at 18:07

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