The impact of area deprivation on diVerences in health: does the choice of the geographical classification matter?

Objective—Many studies show the average health status in deprived areas to be poorer and the use of health care to be higher, but there is hardly any information on the impact of the geographical classification on the size of these diVerences. This study examines the impact of the geographical classification on the clustering of poor health per area and on the size of the diVerences in health by area deprivation. Design—Data on self reported health regarding 5121 people were analysed using three classifications: neighbourhoods, postcode sectors and boroughs. Multilevel logistic models were used to determine the clustering of poor health per area and the size of the diVerences in health by area deprivation, without and subsequently with adjustment for individual socioeconomic status. Setting—General population aged 16 years and over of Amsterdam, the Netherlands. Main outcome measures—Self rated health, mental symptoms (General Health Questionnaire, 12-item version), physical symptoms and long term functional limitations. Main results—The clustering of poor health is largest in neighbourhoods and smallest in postcode sectors. Health differences by area deprivation diVer only slightly for the three geographical classifications, both with and without adjustment for individual socioeconomic status. Conclusions—In this study, the choice of the geographical classification aVects the degree of clustering of poor health by area but it has hardly any impact on the size of health diVerences by area deprivation. (J Epidemiol Community Health 2000;54:306–313) Many studies have shown the average health status to be poorer, and the use of health care to be higher in deprived areas. 28–30 The size and the homogeneity of the areas included in these studies vary considerably, however. Regarding size, several authors argue that smaller areas should result in a more valid, or a more stable measurement of area deprivation. A disadvantage of the use of smaller areas may be, however, that measurement error will increase. Available studies show that health diVerences by area deprivation diVer only slightly if smaller areas are used. This holds for (larger/smaller unit and population size) mortality in Great Britain (electoral ward (EW): 25 000/enumeration district (ED): 500) ; mortality in Perth, Australia (zip code: 2500/collector district: 500); and self rated health in the USA (zip code: 25 000/ census tract: 5000). Furthermore, smaller areas do not yield better results if compared with individual socioeconomic data, if EDs are compared with EWs, or census tracts with zip codes. Regarding homogeneity, contextual, area bound, factors may have a greater impact on health if an area relates to a socioculturally homogeneous, “real”, community. Macintyre and coworkers divide such contextual factors into five broad groups: physical features, quality of the domestic and working environment, the provision of various services, sociocultural features, and the reputation of areas. 38 If a geographical categorisation is solely logistic (like postcodes, which were derived from walking routes of postmen), the resulting areas will mostly be heterogeneous socioculturally. In that case, contextual factors that lead to area health diVerences are unlikely. Of course, homogeneity and size are often inversely associated, but smaller randomly composed areas can still be socioculturally heterogeneous. Most of the discussion regarding the impact of the geographical classification on area diVerences has focused on the situation in the United Kingdom, usually in relation to deprivation payments for general practitioners (GPs). In the UK three distinct geographical classifications are of interest: the EW, the ED and the postcode sector (PS). At present, the Jarman remuneration system in England, Wales and Northern Ireland is based on EWs, albeit with diVerent thresholds and indicators. In Scotland, it is based on PSs (average population: 5000), but in Scotland these are more socioculturally homogeneous than elsewhere in the UK. In the Netherlands deprivation payments for GPs have been introduced recently. For practical reasons, this system is based on PSs, 42 though research on diVerences in health and use of health care by area deprivation almost entirely concerns neighbourhoods or combinations of neighbourhoods (boroughs). 7 14 20 21 24 No information exists on the impact of the geographical classification on the degree of clustering of poor health and little information is available on its impact on the size of area health diVerences in health and use of health care. 27 36 This study therefore examines the impact of the geographical classification on the J Epidemiol Community Health 2000;54:306–313 306 TNO Prevention and Health, Department of Public Health, PO Box 2215, 2301 CE Leiden, the Netherlands