[R] Should I use T-test or prop.test

Dieter Menne dieter.menne at menne-biomed.de
Mon Jan 3 08:44:33 CET 2011

Az Ha wrote:
> I have a set of data where two groups of animals walk around in an
> environment and I have calculated the percentages of the area covered by
> them. Each group covers different area, for example the arithmetic mean is
> 35% and 23% with n=40 and 29 respectively.
> ...
> Should i use unpaired T-test or prop.test?
> ..

Distribution questions aside, you should also consider what your story is.
>From the animal's viewpoint, a doubling from 1% to 2% is as good as one from
30% to 60%, so the proportion is the measure of success.

If you are an ecologist, a change in population from 30% to 60% might be
close to disaster for the environment, so percentage points (60-30)  or
(2-1) is the right choice.


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