Reliability of multiple-component measuring instruments: improved evaluation in repeated measure designs.

A covariance structure analysis method for improved point and interval estimation of composite reliability in repeated measure designs is outlined that accounts for specificity variance. The approach also permits the testing of time-invariance in reliability of multiple-component instruments in terms of the ratio of 'pure' measurement error variance to observed scale score variance. In addition, the procedure allows interval estimation of the difference in composite reliability coefficients across assessment occasions. The method described is illustrated with data from a cognitive intervention study.