----- Original Message -----
From: jkroger <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Sunday, August 20, 2000 9:10 AM
Subject: Which statistical test?
> 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 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. 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. The conditions
> in which A - B is minimal still have significant t's of 5 or 8 (when a p
> of .05 requires a t of around 2).
>
> So according to the test I've chosen, A-B in almost all of the conditions
> is significant. What test will allow me to reveal the much greater
> significance of condition #1 relative to the others? I thought of
> chi-square (sum(A), sum(B) for all intervals; crossed with 1-8), but as
> chi-square is for frequency data, I'm not sure if it's applicable here.
>
> Thanks for any guidance,
> Jim
_______________________________________________________
How can you possibly do this without first modeling the causes, and see if
different approaches describe the data?
How can you assume that the timecourse measures have any validity in the
first place?
DAHeiser
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