Asian Journal of Applied Sciences1996-3343xxxx-xxxxKnowledgia Review10.3923/ajaps.2012.371.383ChandrasekaranV. GopalG. BasileaW. 6201256Many authors have studied the determination of sample size in longitudinal studies under different situations. A statistical methodology for determining the minimum sample size required for within-subjects repeated-measures design, applying Hotellings T2 analysis under the general covariance structure exists. This procedure is extended to between-subjects repeated measures design when there are two treatment groups, assuming the correlation structure among the repeated measures are autoregressive or compound symmetry. Three possible methods of analysis POST, CHANGE and ANCOVA are used to determine the sample size under the assumption that the correlation structure is compound symmetry. In this paper, we extend the existing method to obtain minimum sample size assuming that the correlation structure is first order autoregressive or a random effects model.]]>Akanda, M.A.S., M. Khanam and M.A. Islam,2005512141218Albert, P.S.,19991817071732Antoine, R., A. Sahai and P. Chami,20077951957Chandrasekaran, V., G. Gopal and A. Thomas,20052411391151Dixon, W.J.,1992Pages: 1504Pages: 1504Fleiss, J.L.,1986Frison, L. and S.J. Pocock,19921116851704Laird, N.M. and J.H. Ware,198238963974Machin, D. and M.J. Campbell,1987Matthews, J.N.S., D.G. Altman, M.J. Campbell and P. Royston,1990300230235Nath, D.C. and A. Bhattacharjee,20114640648Nikfar, S., R. Rahimi and M. Abdollahi,20106638644Nugraha, J.,20114113127Ojo, J.F., T.O. Olatayo and O.O. Alabi,20081481491Olaomi, J.O. and A. Ifederu,200811423Senn, S., 199413197198Snedecor, G.W. and W.G. Cochran,19807th Edn.,Pages: 507Pages: 507Ware, J.H.,19853995101Wu, M.C. and K.R. Bailey,198945939955