Validity and power investigation of a test for serial correlation in univariate repeated measures analysis

A common design in biostatistics and psychometrics is the repeated measures design. A popular example is a clinical trial with one grouping factor, e.g. treatment or drug, and one repeated measures factor, e.g. time or visit. For selected ‘real world’ parameter sets, we performed a validity and power study on a test for serial correlation in repeated measures analysis and also conducted a similar study of a test for sphericity. Simulation showed that the serial correlation test identified the serial correlation structure, whereas the sphericity test, for some parameter sets, failed to detect this non‐spherical pattern as often as 85 per cent of the time.