Re: SPSSINC SUMMARY TTEST appears to use critical z when computing CI

Posted by Bruce Weaver on Aug 10, 2022; 6:08pm
URL: http://spssx-discussion.165.s1.nabble.com/SPSSINC-SUMMARY-TTEST-appears-to-use-critical-z-when-computing-CI-tp5741035p5741037.html

Ah, I see.  I just did not understand what was intended by "asymptotic" and "exact".  And if I had looked more carefully at the "exact" CI, I would have noticed that it matched the ordinary (equal variances) CI.  Thanks Jon.  

jkpeck wrote

Using your data, I ran the standard t test procedure and SUMMARY TTEST.  The results were exactly the same up to 5 significant figures.

Note that SUMMARY TTEST shows two sets of CI numbers.  The first set, labelled Asymptotic, and, hence is based on the normality assumption, but the second set, labelled Exact, matches the standard ttest.  Both are displayed for didactic reasons.