Examining the relationship between SIDS and climate using hurdle, ZIP, and finite mixture models
by
Michelle Dalrymple
Department of Mathematics and Statistics, University of Canterbury
Coauthors: Irene Hudson, Rodney Ford

Sudden infant death syndrome (SIDS or cot death) is the sudden and unexplained death of an infant. This study examines the incidence of SIDS in Canterbury (1973 – 1989) in relation to climate. Mixture modelling is a novel approach to probing this relationship.

Three mixture models (hurdle, zero-inflated Poisson (ZIP), and finite mixture) are used as methods which are able to highlight differential effects of climatic covariates between months of SIDS and no SIDS. These methods accommodate the extra zeros, heterogeneity and autocorrelation found in the SIDS series. Mixture models are comprehensive methods applicable to many discrete chronological series including the Canterbury SIDS data. This analysis leads to a better understanding of the effect of climate on SIDS deaths.

Results showed a deviance temperature (a measure of extreme change from the average) is important in months of no SIDS. Months where there is a high deviance temperature leads to increased risk of SIDS compared to months where the temperature has remained reasonably constant. This finding is indicative of hyperthermia, or overheating, of infants leading to increased SIDS risk. Correspondingly in months where SIDS deaths occur, increased humidity leads to increased risk of SIDS.

Date received: September 4, 2001