Eval. Program Plann., 2 (3) (1979), pp. 197-207 View PDFView articleView in ScopusGoogle Scholar [40] D. Hedeker, R.D. Gibbons, C. Waternaux Sample size estimation for longitudinal designs with attrition: comparing time-related contrasts between two groups J. Educ. Behav. Stat., 24 ...