Abstract
Lemonte and Cordeiro [Birnbaum–Saunders nonlinear regression models, Comput. Stat. Data Anal. 53 (2009), pp. 4441–4452] introduced a class of Birnbaum–Saunders () nonlinear regression models potentially useful in lifetime data analysis. We give a general matrix Bartlett correction formula to improve the likelihood ratio (LR) tests in these models. The formula is simple enough to be used analytically to obtain several closed-form expressions in special cases. Our results generalize those in Lemonte et al. [Improved likelihood inference in Birnbaum–Saunders regressions, Comput. Stat. Data Anal. 54 (2010), pp. 1307–1316], which hold only for the (
linear regression models. We consider Monte Carlo simulations to show that the corrected tests work better than the usual LR tests.
Acknowledgements
We gratefully acknowledge grants from FAPESP and CNPq (Brazil), and Mobility Program of the Universidad Industrial de Santander (Colombia). We thank an anonymous referee for helpful comments.