This paper presents a Bayesian method for the analysis of toxicological mul
tivariate mortality data when the discrete mortality rate for each family o
f subjects at a given time depends on familial random effects and the toxic
ity level experienced by the family. Our aim is to model and analyse one se
t of such multivariate mortality data with large family sizes: the potassiu
m thiocyanate (KSCN) tainted fish tank data of O'Hara Hines. The model used
is based on a discretized hazard with additional time-varying familial ran
dom effects. A similar previous study (using sodium thiocyanate (NaSCN)) is
used to construct a prior for the parameters in the current Study. A simul
ation-based approach is used to compute posterior estimates of the model pa
rameters and mortality rates and several other quantities of interest. Rece
nt tools in Bayesian model diagnostics and variable subset selection have b
een incorporated to verify important modelling assumptions regarding the ef
fects of time and heterogeneity among the families on the mortality rate. F
urther, Bayesian methods using predictive distributions are used for compar
ing several plausible models.