Re: Confidence interval is mathematically equivalent to hypothesis test

[Dr. Oliver Walter]

Am 14.10.2018 um 08:46 schrieb John Darrington:

> AGGREGATE OUTFILE * MODE ADDVARIABLES
>      /BREAK=g
>      /Mean = mean(V)
>     /sd = sd(v)
>     /n = n(v)
>     .
>
> compute ci_upper=mean + sd/sqrt(n).
> compute ci_lower=mean - sd/sqrt(n).
>
> list.

Sorry for interrupting, but this doesn't give a 95% (or 90%) CI, but 
only mean +/- one standard error which is a 68%-CI if X is normally 
distributed and sd equals the population variance or an approximate 68% 
CI if the sample size goes to infinity (is large). You have to include a 
t value into the equation for calculating a 95% (or 90%) CI. If your 
sample sizes are small and differ from each other you should use 
different t values for each CI and each group. If you sample size is 
large you could use one z value (1.96) for all groups, but this is not 
appropriate in this case (n1 = n2 = 15, sample sizes are too small for 
this standard normal approximation).