Ecological association between suicide rates and indices of deprivation in the north west region of England: the importance of the size of the administrative unit

Background and objective: Most published research on the ecological relationship between suicide rates and indices of deprivation uses only one level of population aggregation-for example, by local authorities. These ecological associations have been studied at both the local authority and the electoral ward level. Methods: Data on all deaths for which suicide or an open verdict was returned between 1996 and 1998 in the North West Government Office Region (NWGOR) of England (2336 cases) were the subject of this study. These data were provided by the National Confidential Inquiry into Suicide and Homicide by People with Mental Illness. The income and employment indices of deprivation and the population counts were provided by the Department of the Environment, Transport and the Regions, and the Office for National Statistics, respectively. Results: Modelling data at the local authority and ward levels in the NWGOR showed that although at the local authorities level there are no significant associations between suicide rates and two indices, at the ward level there are significant associations. The direction of these associations is such that with an increase in the quartile ranks of each index (ie, with improving the situation of a ward in terms of that index), the rate of suicide decreases. Conclusion: A lack of effect was found once we move from ward to local authority level. This may happen because of the non-homogeneous nature of the local authorities in terms of their income and employment indices. In this sense, wards are more homogeneous. This means that in examining ecological risk factors, a balance was found between large areas (diluted effects but greater power) and small areas.