auda wrote:
>
> Hi, all,
> We are testing a group of subjects on their performance in two different
> conditions (say, A and B), and we are testing them individually. We have an
> alternative hypothesis that reaction time in condition A should be longer
> than in condition B, so we perform a one-tailed t test. However, for some
> subjects, they showed the pattern reverse to our alternative hypothesis--RT
> B> RT A, and the p value is significant under one tailed test.
>
> Could we claimed that these "reversed" subjects showed "significant" results
> in the opposite direction, or we should treat them as non-significant
> results?
If you do a one-tailed test, no. The fact that you are entertaining this
possibility suggests you should be using a two-tailed test. The one-tailed
test has no power to detect differences in the discounted (non-predicted)
direction hence should only be used when you would reject such a finding a priori.
I'm a bit puzzled as to why you test each participant individually? You'd
expect (unless the effect is huge) for some participants to go against the
average pattern. If you do need to test each person individually you need to
use the two-tailed non-directional test and use a correction for multiple
testing (e.g., Bonferonni or similar).
Thom
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