Table 2.

Illustration of the non-decaying (exchangeable) and decaying within-cluster correlation structure implied by the random-effects model in cross-sectional, closed-cohort, and open-cohort designs.

Note: In each correlation matrix, each block represents the correlation structure in a given cluster-period or between two cluster-periods, and the total number of periods is T = 3. The cluster-period sizes are assumed to be equal (N_ij = 2). In the open-cohort design, we assume only one individual is followed through all periods, and a new individual will be supplemented in each period. Each correlation matrix is defined for the vector of observations collected across all periods in the same cluster.