Radford Neal wrote:
>
> The difference is that when dealing with real data, it is possible for
> two populations to have the same mean (as assumed by the null), but
> different variances. In contrast, when dealing with binary data, if
> the means are the same in the two populations, the variances must
> necessarily be the same as well. So one can argue on this basis that
> the distribution of the p-values if the null is true will be close to
> correct when using the pooled estimate (apart from the use of a normal
> approximation, etc.)
>
But, if the null hypothesis is that the means are the same, why
isn't(aren't) the sample variance(s) calculated about a pooled
estimate of the common mean?
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