Thursday, February 7, 2008

Constant Temperatures Means no Warming? A Question of Type-2 Error

I just heard on the radio today global temperatures have been statistically stable since 2001. As someone who said he's become a believer, what am I to make of this?

I'll admit I'd like to know what the margins of error are. I'll also admit those errors are type-1 errors (they measure the probability that we falsely reject the null hypothesis of no change) and are not reflective of the error that we incorrectly reject the alternative, that warming is happening.

Do I like that we don't know the type-2 error probabilities? No. On the other hand, I know mathematically it has been minimized though the use of valid statistical testing. But remember--"minimized" could mean a 95% of incorrectly saying there is no warming.

It's time we remember R A Fisher established 95% Type-1 errors as significant without any hard statistical reasons. Of course, the above link also notes there is a case to be made for a line in the sand (although 95% is merely one line amongst many we could chose), I would argue it is not as important to stick dogmatically to one line in the sand as to simply be clear about the significance level of the results and let the user draw their own conclusion. Perhaps I am, given my ambivalence about Type-2 errors, ready to accept global warming at the 90% or even 85% levels.

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