Methods

The cases were extracted from the medical summaries of sequential emergency medical admissions through the casualty departments at The Royal London Hospitals in 1991–1992. Patient records with a diagnosis of asthma or chronic obstructive airways disease, and resident in Tower Hamlets, were identified. Individually matched controls (also obtained from emergency medical admissions through the casualty departments) with a non-chest related illness were selected based on sex, year of admission and consultant team. The selection method of these controls precludes surgical, orthopaedic or trauma cases. Overall, 82% of the pairs were matched to within five years, the remainder to within 10 years. For each case and control, address, ethnic group, whether there had been treatment in intensive therapy, and whether there had been any re-admission during that year, were extracted. Smoking data were too incomplete to be used.

Using the Address-point software the addresses of cases and controls were expressed as a grid reference for all but eight participants. This software allows each postal address to be located to the “front …