By conditioning on the total number of deaths in the vehicle, each vehicle contributes a multinomial probability: (2) … which calculates the probability that each of the vehicle occupants has the j th outcome.3 As in conditional logistic regression, gi need no longer be estimated, and the behavior of the conditional likelihood estimates for b can rely on the asymptotic properties of the sample size for the number of vehicles, rather than the small sample size within each vehicle. […] only crashes in which there is variability in xijk among the j occupants provide information about the effect of the k th covariate on risk of death. […] we further restricted the data to child-only sets and estimated an RR of 0.30 (95% CI=0.22, 0.41) based on 1188 sets.