[An analysis of mortality in small areas: the problem of residency]

This study was designed to assess the influence of residence misclassification in small areas mortality analysis. Data from a health area in the Valencian Community, which has high mortality from coronary diseases (ICD410-414) has been used. Deaths occurred during 1988 (n = 190) have been divided, using the information reported in the Boletín Municipal de Defunción in two groups: with (n = 109) and without (n = 81) private residence in the area. The Standardized Mortality Ratio (SMR) for the studied diseases was 219.8 (CI 95%: 257.6; 182) for males and 174.8 (CI 95%: 218.7; 130.9) for females. When deaths of persons without residence in the area subtracted from the numerator a change in the SMRs is observed to 120.8 (CI 95%: 149.3; 92.3) in males and 135.9 (CI 95%: 175; 96.2) in females. The excess in coronary heart diseases observed in the area could be partially explained by the "Benidorm-Effect" produced by an important volume of foreign residents with a high risk of dying from these diseases which are not included in the area census.