On Sun, 20 Aug 2000, jkroger wrote:
> Hello, I am trying to determine a statistical difference, but am having
> some difficulty determining what test should be used.
There are competent statisticians at your university, and I believe they
operate a statistical consulting service. You would do well to consult
them.
> 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).
Not to put too fine a point on it, it sounds rather as though the only
statistical test you are familiar with is some variety of t-test, and you
are trying to shoehorn your data into conformance with those constraints.
You evidently have not modelled the situation in statistical terms,
corresponding to your verbal description of your mental model. Until you
can do so, any reasonable solution to your problem will remain outside
your grasp, and it will be extraordinarily difficult for anyone to be of
much help to you via e-mail. Perhaps one or two (additional?) courses
in statistics would be salutary: inquire of your faculty advisor(s)
and/or the statistics department.
< snip, the rest >
-- DFB.
------------------------------------------------------------------------
Donald F. Burrill [EMAIL PROTECTED]
348 Hyde Hall, Plymouth State College, [EMAIL PROTECTED]
MSC #29, Plymouth, NH 03264 603-535-2597
184 Nashua Road, Bedford, NH 03110 603-471-7128
=================================================================
Instructions for joining and leaving this list and remarks about
the problem of INAPPROPRIATE MESSAGES are available at
http://jse.stat.ncsu.edu/
=================================================================
