Application Of Linear Mixed Model Of Repeated Measurements In Medical Study

In many fields of medical studies, the analysis and design of repeated measurements data are often come across. Because of correlation among repeated measurements data and its hierarchical error, it is not suitable to use ordinal method.In this paper, the linear mixed-effects model of repeated measurements is discussed, and the repeated measurements data obtain reasonable results by the fixed and random effects along with efficient estimate of covariance matrix. The linear mixed-effects model presented by Laird and Ware(1982) is a more flexible model for repeated measures. Upon substitution, the linear mixed-effects model can be always expressed in terms of the two stage model and vice-versa. In addition, the linear mixed-effects model also provides greater flexibility with respect to the assumed variance-covariance structure.In this paper, alternative covariance structures are discussed,as well as how to obtain estimates of parameters by solving the mixed model equations.All the medical data collected in the paper were analyzed on computer by the PROC MIXED of SAS software system. Satisfactory conclusions and presentations have been obtained. It is wished that the theoretical basis might have beenfulfilled for the popularized application of the linear mixed-effects model in medical studies.