Diagnostic techniques in generalized estimating equations

We consider herein diagnostic methods for the quasi-likelihood regression models developed by Zeger and Liang [Zeger, S. L., Liang, K.-Y., 1986, Longitudinal data analysis for discrete and conti-nuous outcomes. Biometrics, 42, 121–130.] to analyse discrete and continuous longitudinal data. Our proposal generalises well-known measures (projection matrix, Cook's distance and standardised resi-duals) developed for independent responses. Moreover, half-normal probability plots with simulated envelopes were developed for assessing the adequacy of the fitted model when the marginal distributions belong to the exponential family. To obtain such a plot, correlated outcomes were generated by simulation using algorithms described in the literature. Finally, two applications were presented to illustrate the techniques.