Re: Doesn't a t-test work here?

z wrote:
what they're getting act, i think, is that if a t-test is designed to
be significant or not at the .95 level, that means that 1 time out of
20 it will show a significant difference when there is really no
difference between the treatments, out of random "noise". this is the
generally accepted level of error. however, what you are doing is
basically 10 t-tests simultaneously, so your chance of finding a
significant difference somewhere when in fact there are none at all is
1-(.95)^10, or about .4, if you treat each t-test as though it were
alone and require a .95 confidence limit. this kind of error rate is
obviously a bit high.

The 10 tests aren't independent, so you can't calculate the chance of finding a significant difference that way.
.

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