Abstract
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.
Acknowledgements
We are grateful to Professor Júlio da Motta Singer of the Institute of Mathematics and Statistics, University of São Paulo, for revision and useful comments on a previous version of the article. The research was partially supported by FAPESP—Brazil (01/00098-3).