Date: Tue, 26 Jan 2010 07:10:11 -0800
Reply-To: Bruce Weaver <firstname.lastname@example.org>
Sender: "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From: Bruce Weaver <email@example.com>
Subject: Re: t-test with small n
Content-Type: text/plain; charset=us-ascii
> we are dealing with survey data for two independent groups we would
> like to compare. Due to missing values we have very small and unevenly
> distributed data for some parts of the survey (e.g. 5 responses for
> one group, 8 responses for the control group, answers on likert
> scales). We have a discussion whether a t-test can be used to compare
> these two groups.
> We assume that is is not appropriate to use the t-test but we would
> like to understand the exact nature of the problem. We are aware of
> the requirments for the t-test like normal distribution, equal
> variances etc. We are also aware that this test has a low test-power,
> however when we try it out the test turns out to be significant.
> What would be the correct argument to refuse using the t-test for this
> situation (if it is to be refused?). Is it just because we are having
> difficulties to prove that we meet the requirements? What would you
> consider a lower boundary that justifies to use a t-test? Would it be
> more appropriate to use a non parametric test or is it just impossible
> to show a systematic difference with a small N like this?
> Thanks a lot for your input.
You might find this BMJ note useful.
"When all else fails, RTFM."
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