SEE response to similar question that I posed in May. Scroll all the way down to read how I described the sample size issue then.....thanks!

PS: if anybody remembers having commented on the below matter relative to PANEL analysis please let me know...thanks!

In a message dated 10/26/2006 8:48:08 P.M. Eastern Standard Time, Rcarlstedt writes:

I'll try to find the post and response about PANEL analysis that I received previously that implied that one could use/enter trait constants each time other more variable predictor variables are entered.

Yes, that is by definition a time-invariant variable and that is how it is handled in a mixed models approach.

Paul R. Swank, Ph.D. Professor, Developmental Pediatrics Director of Research, Center for Improving the Readiness of Children for Learning and Education (C.I.R.C.L.E.) Medical School UT Health Science Center at Houston

-----Original Message----- From: SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU] On Behalf Of Rcarlstedt@aol.com Sent: Monday, May 15, 2006 1:09 PM To: SPSSX-L@LISTSERV.UGA.EDU Subject: Sample Size Issues

I have a methodological question pertaining to sample size.

If one has a small sample in which specific measures are considered TRAITS, that is, they are considered to be stable longitudinal mediators of certain behaviors and outcome measures can they be seen/used as repeated measures in a study that is interested in their influence on other outcome measures?

For example, I have longitudinal data spanning nine months (a small sample of athletes). I have repeated measures (81; ca. 10 per subject) on heart rate variability (HRV) and numerous statistical outcome measures (e.g., games won or lost)....over ten measurement occasions (matches) and pre-post HRV measurements associated with these matches. In addition, I have neuropsychological/cognition measures that are also considered stable for the same sample. I also have intervention efficacy data obtained in the context of an ecologically more valid and not a controlled design.

Both cognition and personality/behavioral measures were found to explain varying amounts of variance explained in outcome measures and vice-versa. Also, among and between variable.

The sample size was only 8-12. However, data points or repeated measures for outcome measures ranged from 52-81. Thus, although I only had a sample of around 10, I have up to 81 outcome measures.

My question: if my cognition and personality/behavioral measures are considered stable, can they be entered as predictor variables equivalent to the amount of measurement occasions multiple times? For example, if player A played 10 matches and 10 HRV measurements were taken, can one justifiably enter his or her cognition-personality scores ten times to match the outcome measurements; under the assumption that these stable traits are enduring and will indeed influence HRV and performance outcome measures at different points in time (the predictor measures have very high Test-Retest reliability)?

This would increase sample size/predictor data points from 8 to 81, albeit the predictor and outcome measures would be from a limited sample?

Is this more a theoretical or methodological issue or can one justify such an approach because stable predictor variables will "always" influence certain performance (at the intra and inter-individual level)? Which my results demonstrated.

What about vice versa when looking at how HRV and outcome is associated with cognition/personality measures (only 8 measures/8 subjects), whereas the HRV/Outcome measurement involves 52-81 measurement occasions.

Any feedback would be appreciated including statistical considerations, limitations, alternative data-analysis suggestions etc.

Thanks!

RC

____________________________________________ Roland A. Carlstedt, Ph.D. Licensed Clinical Psychologist/Licensed Applied Psychologist Chair, American Board of Sport Psychology Clinical and Research Director: Integrative Psychological Services of NYC Research Fellow in Applied Neuroscience: Brain Resource Company _www.americanboardofsportpsychology.org_ (http://www.americanboardofsportpsychology.org/) rcarlstedt@americanboardofsportpsychology.org 917-680-3994