Psychiatric admissions and aircraft noise from London Airport: four-year, three-hospitals' study.
Nine thousand persons admitted to three large psychiatric hospitals, over a period of four years, were classified according to the aircraft noise exposure of their home address, using the Noise and Number Index. The analysis searched first for simple associations between exposure and admission rates, then for complex interactions with socio-economic characteristics of the area of residence. There was no common pattern of admissions across the three hospitals: in one case the rates decreased with aircraft noise; in the other two the rates increased with noise exposure. However, since in all cases the trends could be attributed to non-noise factors characteristic of the population, it was concluded that the effects of noise, if any, could only be small, weakly influencing other causal variables but not overriding them. Further analyses showed that positive associations between noise and admissions occurred in some groups and in some districts. People 45 years old and over exhibited higher admission rates than expected in the highest noise zone in one hospital. The districts where a positive trend between noise and admissions was evident were those with a higher proportion of one-person households, a higher proportion of immigrants, or a higher proportion of professionals and managers; however, these results were only found in one hospital with counterexamples in others. No strong, significant noise effect could be found. Limitations of the hospital records and specific difficulties in setting up the data for these studies are discussed.