手法を比較

	生態学的研究	コホート研究
分野	疫学	疫学
系統	Process / pipeline	Process / pipeline
提唱年	19th century (Snow 1854); formalised mid-20th century	Mid-20th century (formal epidemiological design codified ~1950s)
提唱者	Various; foundational work by John Snow (1854) and systematised in modern form by Brian MacMahon and colleagues	Doll & Hill (British Doctors Study, 1951); Snow (cholera, 1854)
種類	Observational epidemiological study	Observational longitudinal study design
原典	Morgenstern, H. (1995). Ecologic studies in epidemiology: concepts, principles, and methods. Annual Review of Public Health, 16(1), 61–81.	Rothman, K. J., Greenland, S., & Lash, T. L. (2008). Modern Epidemiology (3rd ed.). Lippincott Williams & Wilkins. ISBN: 978-0781755641
別名	aggregate study, correlational study, ecological correlation study, population-level study	longitudinal study, follow-up study, panel study, incidence study
関連	5	6
概要	An ecological study is an observational epidemiological design in which the unit of analysis is a group or population — a country, region, city, or time period — rather than an individual. Exposures and outcomes are measured as aggregates (rates, proportions, or means) and then correlated across groups to generate or evaluate hypotheses about population-level associations between risk factors and disease.	A cohort study assembles a group of individuals who share a common starting point — typically freedom from the outcome of interest — and follows them over time to observe who develops the outcome. By comparing incidence rates between exposed and unexposed subgroups, researchers can estimate relative risk and absolute risk differences. Cohort studies are the gold-standard observational design for measuring disease incidence and establishing temporal relationships between exposure and outcome.