Repeated‐measures model for the investigation of temporal trends using longitudinal family studies: Application to systolic blood pressure

A contemporary path model for the analysis of familial resemblance is extended to incorporate repeated measurements on the entire pedigree over time, in order to assess age‐related changes in familiality. The parameters of the model can be defined as arbitrary functions of the ages, age differences, or cohabitation times of the family members at the exact time of measurement. Tracking of the phenotypes is decomposed into a familial and a nonfamilial component, which vares with both the time span between measurements and the ages at measurement. Some of the family members may have data missing on one or more visits, and the visits may be unequally spaced both within and across families. The method incorporates all measurements available from all visits into a single model. The model is applied to longitudinal data on systolic blood pressure in 490 East Boston families measured two times at 3‐year intervals. Evidence for some nonfamilial tracking is found. Additionally, significant temporal trends are demonstrated in the familiality as a function of age, t²(A), which appears to be near zero at birth, grow to a maximum of about 40% at around age 30, and then appears to monotonically decrease again. No evidence was found for temporal trends in marital resemblance or residual sibling environmental effects. This model provides an objective method of investigating developmental changes in the correlational structure of families over time using repeated‐measures and of estimating continuous changes in familiality with age.