Overview of Linear Fixed Models for Longitudinal Data

Abstract

In a longitudinal setup, a small number of repeated responses along with certain multidimensional covariates are collected from a large number of independent individuals. Let y _yi1, …,y _it , …,y _{iT i} be T _i ≥ 2 repeated responses collected from the ith individual, for i = 1, …, K, where K → ∞. Furthermore, let x _it = (x _{it 1} , …,x _{it p} )^′ be the p-dimensional covariate vector corresponding to y _it , and β denote the effects of the components of xit _it on y _it . For example, in a biomedical study, to examine the effects of two treatments and other possible covariates on blood pressure, the physician may collect blood pressure for T _i = T = 10 times from K = 200 independent subjects.