Calculating the Test-Retest Reliability Co-efficient from Normative Retest Data for Determining Reliable Change
A. D. Hinton-Bayre · Archives of Clinical Neuropsychology · 2010
Please note in the setting of a test (X) and retest (Y) control group, rXY is the test-retest reliability coefficient, σX the estimated initial standard deviation (σ2 is a variance), σY the estimated retest standard deviation, MY the retest mean, MX the initial test mean, t the repeated-measures student's t-test, and n the sample size. If an ANOVA (F)-statistic is presented, the reader should recall that in the two-group example, t = √F. Researchers in the field of repeated or longitudinal data collection are encouraged to present basic test-retest statistics including reliability estimates, or at least exact inferential statistics. This simple and essential reporting will readily allow the use of RC models to assess individual change. Of course, the clinician should always be mindful that the control group adequately match the individual in terms of characteristics, initial test scores, and test-retest interval. The author is willing to supply a spreadsheet file to facilitate the calculation of RC models reported in Hinton-Bayre (2010) and the above expression on request.