Objectives: To study the geographical pattern of mortality caused by haematological tumours in Spain at the municipal level using three Bayesian models and to compare their goodness of fit.
Methods: The fitted Bayesian hierarchical models were: (1) the Besag York and Molliè (BYM) model; (2) a model based on zero-inflated Poisson (ZIP) distribution, which allowed a large number of event-free areas; and (3) a mixture of distributions that enabled discontinuities (jumps in the pattern) to be modelled. The three models allow smoothed relative risk maps to be obtained for the all countries. The goodness of fit was evaluated using the deviance information criteria.
Results: The three models yielded similar results. The ZIP model plotted a pattern almost identical with the BYM model. The goodness-of-fit criteria indicate that the mixture model is the one that best fits our data. Haematological tumours display a geographical pattern that could be partly explained by environmental determinants, as many of the highest-risk towns are located in heavily industrialised areas.
Conclusions: The choice of one or another model has scant practical consequences. The pattern of distribution supports the hypothesis that differences in lifestyles, air/industrial pollution and migratory phenomena may determine the pattern of urban mortality due to these tumours.
- BYM, Besag York and Molliè
- CAR, conditional autoregressive
- DIC, Deviance Information Criterion
- NHL, non-Hodgkin’s lymphomas
- SMR, standard mortality ratio
- ZIP, zero-inflated Poisson
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Funding: This study was financed by Grant Number EPY-1176/02 from the Carlos III Institute of Health (ISCIII) and RCESP FIS-C03/09 (Spanish Network for Cooperative Research in Epidemiologyand Public Health).
Competing interests: None declared.