Multiple choices 21/50
Answer (Choose 1 answer)
B A. Observational study
C B. An experiment.
D C. None of them.
D. Retrospective
In an attempt to study the health effects of air pollution, a group of researchs selected 6 cities in very different environments some from an urban setting (e.g. greater Boston), some from a heavy industrial setting (e.g.eastern Ohio), some from a rural setting (e.g. Wisconsin). Altogether they selected 8000 subjects from the 6 cities, and followed their health for the next 20 years.
This represents what type of study?
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