6. ecological studies外文翻译.pdf

6. Ecological studies | BMJ /about-bmj/resources-readers/publicati... Helping doctors make better decisions Most epidemiological investigations of aetiology are observational. They look for associations between the occurrence of disease and exposure to known or suspected causes. In ecological studies the unit of observation is the population or community. Disease rates and exposures are measured in each of a series of populations and their relation is examined. Often the information about disease and exposure is abstracted from published statistics and therefore does not require expensive or time consuming data collection. The populations compared may be defined in various ways. One common approach is to look for geographical correlations between disease incidence or mortality and the prevalence of risk factors. For example, mortality from coronary heart disease in local authority areas of England and Wales has been correlated with neonatal mortality in the same places 70 and more years earlier. This observation generated the hypothesis that coronary heart disease may result from the impaired development of blood vessels and other tissues in fetal life and infancy. Many useful observations have emerged from geographical analyses, but care is needed in their interpretation. Allowance can be made for the potential confounding effects of age and sex by appropriate standardisation. More troublesome, however, are the biases that can occur if ascertainment of disease or exposure, or both, differs from one place to another. For example, a survey of back disorders found a higher incidence of general practitioner consultation for back pain in the north than the south of Britain, which might suggest greater exposure to some causative agent or activity in the north. Closer investigat