Tuesday, November 24, 2009

Evaluating a scientific theory

I mentioned there is a second issue I'd like to raise about the leaked emails between Phil Jones and Michael Mann: how can scientific theories be evaluated by non-specialists?

It is often claimed that they can't, but I don't agree. One of the distinguishing characteristics of a scientific theory is that it makes objective claims that can be evaluated by anyone. You don't have to wear the right regalia or attune yourself with a spirit walk. The theory should make objective claims, and the experiments should be repeatable.

For that matter, full-time workers in an area have challenges compared to an outsider. One is that they tend to be highly specialized, and thus not familiar with the arguments supporting the foundational issues of a field. For example, practically no one working on programming language design spends a lot of time really studying why it is that computers have proven useful in the larger economy. It's just taken for granted. A second problem is that anyone making a living is highly biased in favor of any theory that will keep that living going. PL folks are eager to accept any reason that PL is important.

So outsiders are not only capable, but an important part of the process. What should they do, though? Let me describe two strategies.

First, anyone can evaluate the ultimate predictions of a theory. You don't have to be a Galileo to observe the results of his famous falling bodies experiment. More closely to my world, you don't have to be a football expert to know that the University of Georgia's football team is doing poorly this year. It takes a specialist to make a better theory of gravity, and it takes a specialist to make a good football team, but anybody can look at the results and see whether they are any good or not.

A second approach is to explore the logical implications and structure of a theory. As a simple example, a theory that contradicts itself is clearly problematic. Any theory that concludes both A and not A is a broken theory. More commonly, a theory makes an obscure claim A that implies a more accessible conclusion B. If someone tells you about some interesting property of phlogiston, try to find out what observable implications it has on real fires. It might be that the implication B is plainly false, in which case again the theory is broken. More frequently, B is contentious but not certainly false. Proponents need to either go further out on a limb and accept B, or they need to weaken A so that it no longer implies B. It takes a specialist to choose which way to go, but anybody can evaluate the whole package of logical implications.

That's two ways to evaluate a scientific theory from the outside. Overall, I believe such evaluation is not only possible, but that it's necessary for a scientific field to be healthy.

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