Bivariate Correlated Frailty Models with Varied Variances

Fit and simulate bivariate correlated frailty models with proportional hazard structure. Frailty distributions, such as gamma and lognormal models are supported semiparametric procedures. Frailty variances of the two subjects can be varied or equal. Details on the models are available in book of Wienke (2011,ISBN:978-1-4200-7388-1). Bivariate gamma fit is obtained using the approach given in Kifle et al (2023) with modifications. Lognormal fit is based on the approach by Ripatti and Palmgren (2000) . Frailty distributions, such as gamma, inverse gaussian and power variance frailty models are supported for parametric approach.