Socioeconomic inequalities in mortality in Barcelona: A study based on census tracts (MEDEA Project)
Introduction
Various studies both in Spain and other countries have shown the existence of geographical inequalities in mortality and morbidity, with areas of greater social and material deprivation presenting higher mortality (Benach and Yasui, 1999; Levin and Leyland, 2006; Cooper et al., 2001; Borrell et al., 1997; Benach et al., 2001). The analysis of small geographical areas allows us to identify and analyse social- and mortality-related geographical patterns in detail, as well as to detect areas susceptible of intervention (Domínguez-Berjón, 2002; Adams-Jones et al., 1995; Domínguez-Berjón et al., 2001). In the last decade, studies of mortality in small geographical areas have acquired considerable importance, above all in urban areas where inequalities are usually larger (Borrell and Pasarín, 2004).
The geographical distribution of mortality in small areas is normally presented using maps, where the display of mortality inequalities between different geographical areas is more efficient than through the use of tables of statistics (Martínez et al., 2005). In small geographical areas we may have extreme values of relative risks (both high and low), which dominate the geographical patterns displayed on mortality maps. However, it may be that these extreme relative risks present large variability as a result of reduced population numbers. This high variability affecting mortality indicators in some of the small areas, in our case the standardised mortality ratio (SMR) can be controlled using statistical methods based on a Bayesian approach. In order to estimate the relative risk in a small area, these methods perform a weighting between the information provided by the area in question and that from the rest of areas or neighbouring areas, thus a smoothing of the SMR is obtained (Clayton and Bernardinelli, 1992) that will be more pronounced in those areas having higher variability.
The majority of studies of geographical inequalities in mortality have used larger areas than those of the present study (census tract) (Odoi et al., 2005; Ruiz-Ramos et al., 2004; Nolasco et al., 2004). Those studies have shown the need to have information about health indicators in the most highly disaggregated areas possible. As in other cities, the first studies conducted in Barcelona used municipal districts (10 areas), later neighbourhoods (38 areas) and more recently the Primary Health Care Zones (66 areas) (Borrell and Arias, 1993, Borrell and Arias, 1995; Pasarín et al., 1999). As the unit of analysis got progressively smaller it became possible to detect areas of deprivation, which were masked by the larger territorial units. The census tract may help to detect patterns which would not be evident with other geographical units (Domínguez-Berjón et al., 2005; Domínguez-Berjón and Borrell, 2005). Therefore, the aims of the present study are to describe socioeconomic inequalities (year 2001) and those of mortality (years 1996–2003) in the census tracts of Barcelona and to analyse the relationship between mortality inequalities and the socioeconomic level of these areas.
Section snippets
Design
This study belongs to a project called MEDEA that analyses mortality inequalities at the small area level in different Spanish cities. It is a cross-sectional ecological study. The units of analysis were the 1491 census tracts of the city of Barcelona according to the 2001 Census of Population and Households. In that year, the city of Barcelona had a population of 1,503,884 inhabitants, the census tracts ranging in size from 91 to 7003 inhabitants, with a median of 923.
Study population and information sources
The population under
Results
Table 1 presents the distribution of the population, the deprivation index and the number of deaths caused and by census tract for the city of Barcelona. Note that the deprivation index is normalised with mean 0 and standard deviation 1. Of the total deaths in Barcelona city during the period 1996–2003, 64,530 were men, and 65,628 women. It may be observed that 20% of total mortality is a consequence of the following specific causes: ischaemic heart disease (n=7636) and lung cancer (n=5896) in
Discussion
The present study describes socioeconomic inequalities in mortality by census tract in the city of Barcelona and shows that there is excess of mortality in coastal and northern areas of the city. This distribution is similar to that of socioeconomic deprivation and therefore there is an association between the mortality and socioeconomic indicators, not only for total mortality but also for the majority of the specific causes of death examined. This analysis extends a previous study where we
Acknowlegements
This article was partially funded by FIS Project no. PI042013 and by the ‘Red de Centros de Epidemiología y Salud Pública’ (C03/09).
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