Parapsychologists are constantly protesting that they are playing by all the standard scientific rules, and yet their results are being ignored - that they are unfairly being held to higher standards than everyone else. I'm willing to believe that. It just means that the standard statistical methods of science are so weak and flawed as to permit a field of study to sustain itself in the complete absence of any subject matter.
— Eliezer Yudkowsky, Frequentist Statistics are Frequently Subjective
Imagine if, way back at the start of the scientific enterprise, someone had said, "What we really need is a control group for science - people who will behave exactly like scientists, doing experiments, publishing journals, and so on, but whose field of study is completely empty: one in which the null hypothesis is always true.
"That way, we'll be able to gauge the effect of publication bias, experimental error, misuse of statistics, data fraud, and so on, which will help us understand how serious such problems are in the real scientific literature."
Isn't that a great idea?
By an accident of historical chance, we actually have exactly such a control group, namely parapsychologists: people who study extra-sensory perception, telepathy, precognition, and so on.
There's no particular reason to think parapsychologists are doing anything other than what scientists would do; their experiments are similar to those of scientists, they use statistics in similar ways, and there's no reason to think they falsify data any more than any other group. Yet despite the fact that their null hypotheses are always true, parapsychologists get positive results.
This is disturbing, and must lead us to wonder how many positive results in real science are actually wrong.
The point of all this is not to mock parapsychology for the sake of it, but rather to emphasise that parapsychology is useful as a control group for science. Scientists should aim to improve their procedures to the point where, if the control group used these same procedures, they would get an acceptably low level of positive results. That this is not yet the case indicates the need for more stringent scientific procedures.
Acknowledgements
The idea for this mini-essay and many of its actual points were suggested by (or stolen from) Eliezer Yudkowsky's Frequentist Statistics are Frequently Subjective, though the idea might have originated with Michael Vassar.
This was originally published at a different location on the web, but was moved here for bandwidth reasons at Eliezer's suggestion.
Comments / criticisms
A discussion on Hacker News contained one very astute criticism: that some things which may once have been considered part of parapsychology actually turned out to be real, though with perfectly sensible, physical causes. Still, I think this is unlikely for the more exotic subjects like telepathy, precognition, et cetera.
Huh? "Metaphysics" refers to an incredibly wide variety of claims. But I'd say that metaphysics tries to answer questions about reality that aren't the kind of questions that can be answered by experimental science. Since we lack a good method for answering these questions our confidence in metaphysical claims is usually substantially lower than it is for empirical claims. But why should we think all metaphysical questions are radically different from scientific questions such that the answer to one can't influence our estimations of the other? Of hand I can't think of a number of metaphysical hypotheses that have been greatly effected by scientific knowledge and vice versa-- materialism, substance dualism, determinism and indeterminism, free will, eternalism and philosophies of time etc.
In this case it seems rather obvious that if we are "living in the Matrix" the probability that the basic laws of physics are complicated rather than simple is dramatically higher.
I never denied that a our assessment of an empirical claim may be influenced by the metaphysical views we hold. I simply noted that, once the Matrix hypothesis is understood as a metaphysical hypothesis, it is unclear why believing that we live in the Matrix should increase our credence in the various claims of parapsychology.