LAUSR

A case-crossover analysis is used as a simple but powerful tool for estimating the effect of short-term environmental factors such as extreme temperatures or poor air quality on mortality. The environment on the day of each death is compared to the one or more "control days" in previous weeks, and higher levels of exposure on death days than control days provides evidence of an effect. Current state-of-the-art methodology and software (INLA) cannot be used to fit the most flexible case-crossover models to large datasets, because the likelihood for case-crossover models cannot be expressed in a manner compatible with this methodology. In this paper we develop a flexible and scalable modelling framework for case-crossover models with linear and semi-parametric effects which retains the flexibility and computational advantages of INLA. We apply our method to quantify non-linear associations between mortality and extreme temperatures in India. An R package implementing our methods is publicly available.