  We consider the issue of assessing influence of observations in the class of
Birnbaum-Saunders nonlinear regression models, which is useful in lifetime data
analysis. Our results generalize those in Galea et al. [2004, Influence
diagnostics in log-Birnbaum-Saunders regression models. Journal of Applied
Statistics, 31, 1049-1064] which are confined to Birnbaum-Saunders linear
regression models. Some influence methods, such as the local influence, total
local influence of an individual and generalized leverage are discussed.
Additionally, the normal curvatures of local influence are derived under
various perturbation schemes.
