Alan:
Could you please give us an example of such a situation?
">Consider first a set of measurements taken with
>a measuring instrument whose sampling errors have a known standard
>deviation (and approximately normal distribution)."
Jon
At 01:10 PM 4/20/01 -0400, you wrote:
>(This note is largely in support of points made by Rich Ulrich and
>Paul Swank.)
>
>I disagree with the claim (expressed in several recent postings) that
>z-tests are in general superseded by t-tests. The t-test (in simple
>one-sample problems) is developed under the assumption that independent
>observations are drawn from a normal distribution (and hence the mean and
>sample SD are independent and have specific distributional forms).
>It is widely applicable because it is fairly robust against violations
>of this assumptions.
>
>However, there are also situations in which the t-test is clearly
>inferior to a z-test. Consider first a set of measurements taken with
>a measuring instrument whose sampling errors have a known standard
>deviation (and approximately normal distribution). In this case, with
>a few observations (let's say 1 or 2, if you want to make it very clear),
>the z-based procedure that uses the known SD will give much more useful
>tests or intervals than a t-based procedure (which estimates the SD from
>the data at hand).
>
>snip>
> Alan Zaslavsky
> Harvard Med School
>
>
>
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