2amt0r2024, 19:42 Chapter 6, Ecological studies Intended for healthcare professionals OurCompany Subscribe MyAccount Login hebm Q Home / About BM) / Resourcesforreaders / Publications / Epidemiology forthe uninitiated / Chapter 6, Ecological studies Chapter 6. Ecological studies More chapters in Epidemiology for the uninitiated 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. Geographical comparisons 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 analvses. but care is needed in their . . UAccept Cookies and privacy ee We and our 109 partners store and/or access information ona device, such as unique IDsin cookies to ess personal datz ay ge your choices by clicking including your right to Reject All objec where legitimate interestis used or at any time inthe privacy policy page. These choices wil htips:fiwwybmj comiabout-bmi/tesources-readers/publicalions/epidemiology-uniniiated/6-2cological- studies 182amor20s, 19:42 Chapter 6, Ecologtcal studies hospital and be diagnosed. On the other hand, unbiased ascertainment of disorders such as depression or Parkinson's disease may be difficult without a specially designed survey. When there is doubt about the uniformity of ascertainment, it may be necessary to explore the extent of any possible bias in a validation exercise. Time trends Many diseases show remarkable fluctuations in incidence over time. Rates of acute infection can vary appreciably over a few days, but epidemics of chronic disorders such as lung cancer and coronary heart disease evolve over decades. If time or secular trends in disease incidence correlate with changes ina community's environment or way of life then the trends may provide important clues to aetiology. Thus, the currently increasing incidence of melanoma in Britain has been linked with greater exposure to sunlight (from fashions in dress and holidays abroad); and successive rises and falls in mortality from cervical cancer have been related to varying levels of sexual promiscuity, as evidenced by notification rates for gonorrhoea, Like geographical studies, analysis of secular trends may be biased by differences in the ascertainment of disease. As health services have improved, diagnostic criteria and techniques have changed. Furthermore, whereas in geographical studies the differences are accessible to current inquiry, validating secular changes is more difficult as it depends on observations made and often scantily recorded many years ago. Nevertheless, the reality — if not the true size — of secular trends can often be established with reasonable certainty. The rise and subsequent fall in the incidence of appendicitis in Britain during the past 100 years is a good example. Migrants The study of migrant populations offers a way of discriminating genetic from environmental causes of geographical variation in disease, and may also indicate the age at which an environmental cause exerts its effect. Second generation Japanese migrants to the USA have substantially lower rates of stomach cancer than Japanese people in Japan, indicating that the high incidence of the disease in Japan is, environmental in origin. In first generation migrants rates are intermediate, which suggests that the Cookies and privacy We and our 109 partners store and/or access information on a device, such as unique IDsin cookies to including your right to object where legitimate interest is used, or at any time in the privacy policy page. These choice htips:fiwwybmj comiabout-bmi/tesources-readers/publicalions/epidemiology-uniniiated/6-2cological- studies 21622mt0r2024, 19:42 ‘Chapter 6, Eeologial stu Occupation and social class The other populations for whom statistics on disease incidence and mortality are readily available are occupational and socioeconomic groups. Thus, mortality from pneumonia is high in welders, and the steep social class gradient in mortality from chronic obstructive lung disease is evidence that correlates of poverty, perhaps bad housing, have an important influence on the disease. Chapters ‘+ Chapter 1. What is epidemiology? + Chapter 2. Quantifying disease in populations ‘+ Chapter 3. Comparing disease rates ‘* Chapter 4. Measurement error and bias ‘* Chapter 5. Planning and conducting a survey + Chapter 6. Ecological studies * Chapter 7. Longitudinal studies * Chapter 8. Case-control and cross sectional studies + Chapter 9. Experimental studies + Chapter 10. Screening ‘* Chapter 11. Outbreaks of disease + Chapter 12. Reading epidemiological reports * Chapter 13. Further reading Cookies and privacy We and our 109 part process personal data, You may a where legitimate i rs store and/or access informal ona device, such as unique IDs in cookies tor manage your choices by clicking below, including your right to cy policy page. These choices will be obje sts used, or at any time in htips:fiwwybmj comiabout-bmi/tesources-readers/publicalions/epidemiology-uniniiated/6-2cological- studies22mt0r2024, 19:42 Chapter 6, Ecological studies UK Jobs The Pembridge Villas Surgery: Salaried GP Kent and Medway NHS & Social Care Partnership Trust: Consultant Psychiatrist - Dover Old Age Community Kent and Medway NHS & Social Care Partnership Trust: Consultant Psychiatrist - Folkestone Community North Lambeth PCN: Exciting Opportunity for Newly Qualified GPs King's College Hospital NHS Foundation Trust: Consultant in Medical Microbiology & Infection Services King's College Hospital NHS Foundation Trust: Consultant Haematologist-Special Interest in Stem Cell Transplantation Cookies and privacy We and our 109 part process personal data, You may a where legitimate i rs store and/or access informal ona device, such as unique IDs in cookies tor manage your choices by clicking below, including your right to cy policy page. These choices will be obje sts used, or at any time in htips:fiwwybmj comiabout-bmi/tesources-readers/publicalions/epidemiology-uniniiated/6-2cological- studies ais22mt0r2024, 19:42 Follow us on Twitter Facebook YouTube Rss. Content links Collections Health in South Asia Women's, children’s & adolescents’ health Zika virus Research Education News and views BM) Opinion Rapid responses Archive Resources Authors Reviewers BMA members Readers Subscribers Advertisers and sponsors Media Recruiters Cookies and privacy Chapter 6, Ecological studies About us About us Editorial staff BMJin the USA BMJin Latin America BMJin South Asia Advisers Policies ‘Submit your paper Explore BMJ Our company BM) Careers. BM) Learning BM Masterclasses BM) Journals BM) Student ‘Academic edition of The BM} BM) Best Practice The BM) Awards We and our 109 partners store and/or access information on a device, such as unique IDs in cookies to process personal data. 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