Hi On Mon, 20 Jan 2003, Jeremy Bauer wrote:
> I have 10 subjects, each performing 2 different activities 10 > times. I am looking at the difference in maximum left > foot-ground forces during running and during landing from a > jump. So, I measure foot-ground forces for subject A 10 > times while running and 10 times while landing from a jump. > I want to know if the maximum measured forces are different > between tasks. > I've performed several studies in the past showing that > foot-ground forces do not change as a function of trial. > However, I need to collect 10 trials due to the variance that > exists in foot-ground force measures. In the past, I have > calculated the mean foot-ground force for each subject in > each task, then just used a paired t-test. This seems > reasonable, however while no one has ever told me this > approach is incorrect, no one has told me it is correct. I > basically just don't have much confidence in that approach. 1. Averaging across trials is standard in many, many areas of research, so your approach has a lot of backing. 2. You could calculate cronbach's alpha or some other measure of reliability for the 10 trials of each type. If strong enough, this would justify the average measure and in any case give you some idea of how "typical" the average is of each trial. 3. If you haven't done it in the past, you might want to think about counter-balancing the two measurements (i.e., half subjects do running first and half do jumping first). You could then ignore this difference and persist with your t-tests knowing that order was counter-balanced, or you could include order as a between-subjects factor in a mixed (split-plot) anova. Best wishes Jim ============================================================================ James M. Clark (204) 786-9757 Department of Psychology (204) 774-4134 Fax University of Winnipeg 4L05D Winnipeg, Manitoba R3B 2E9 [EMAIL PROTECTED] CANADA http://www.uwinnipeg.ca/~clark ============================================================================ . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . =================================================================
