A MULTILEVEL MODEL OF SUDDEN-INFANT-DEATH-SYNDROME IN ENGLAND AND WALES

It has previously been shown that there is a significant association b etween mortality from sudden infant death syndrome (SIDS) and rates of long-term migration between local authority districts in England and Wales. This evidence supports the theory that exposure to infections, mediated by population mixing, may be an important factor in many case s of SIDS. In this paper, multilevel modelling is used to examine the variability in SIDS deaths at different geographical scales, namely di strict, county, and regional levels. Given the population-mixing hypot hesis, it is possible that high levels of population mixing in one dis trict will have an effect on the spread of infections in an adjacent d istrict, and the rates for individual districts will not be spatially independent of each other. Factors such as climate varying at regional scale may also be important. A log-linear multilevel model is develop ed to examine these issues, and the discussion focuses on the methodol ogical issues raised by the analysis such as appropriate multilevel st ructure, methods of estimation, dispersion of residuals, and significa nce of parameter estimates.