jkroger wrote:
>
> Hello, I am trying to determine a statistical difference, but am having
> some difficulty determining what test should be used.
>
> I have two timecourse measures, A and B. At 20 consecutive intervals, A
> and B are measured, and the results are plotted. Both signals rise quickly
> to about the same height, then fall. Sometimes A stays elevated longer.
>
> There are eight seperate trials (representing eight conditions), producing
> eight pairs of curves.
>
> I want to show that in some conditions, the difference between the length
> of A's response and B's response is greater than in other conditions:
> duration(A) - duration(B) is significantly greater in some conditions.
>
I assume by duration you mean the time spent at the maximum height. In
that case, you are only interested in that part of the curve. If you
plot (B-A) against time, does that give you a clear enough picture?
> I tried a t-test for each condition, subtracting B from A at each interval
> and using a t-test to determine if the resulting sample differed from 0.
> Unfortunately, in a couple conditions where it appears the A response is
> about the same as the B response, but the t-test is so sensitive that even
> small differences between A and B produce significance.
Could this be because there is a significant difference elsewhere?
Again, time series plots of (B-A) will help.
The t value for
> the condition (#1) which it is important to demonstrate has a longer A
> duration (as is clearly obvious on inspection) is over 38.
If it's clearly obvious on inspection, then why not just plot the
graphs, and not bother with stats tests?
If it's not so clear that even a politician would see it, you could
think about just testing the observations after the maximum, for
example. It's perhaps slightly ad hoc, but if you can justify a test
like that, then it might be sufficient.
Bob
--
Bob O'Hara
Metapopulation Research Group
Division of Population Biology
Department of Ecology and Systematics
PO Box 17 (Arkadiankatu 7)
FIN-00014 University of Helsinki
Finland
tel: +358 9 191 7382 fax: +358 9 191 7301
email: [EMAIL PROTECTED]
To induce catatonia, visit:
http://www.helsinki.fi/science/metapop/
I have yet to see any problem, however complicated, which, when you
looked at it in the right way, did not become still more complicated. -
Poul Anderson
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