Comparisons of individual- and aggregate-level analyses of data from a multigroup observational study are made using an exponential form relative rate model. Stratified, analytic random effects, and aggregate random effects analyses are studied. Estimating equations are developed to give a consistent estimation procedure across analyses and corresponding information matrices are compared. Simulation studies provide insight into the efficiency and bias of relative rate parameter estimates with respect to covariate dispersion, confounding, and covariate measurement error.