Epidemiology for Public Health Practice 5th Edition by Robert Friis,Thomas Sellers

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The following question lists examples of observational studies. Indicate the type of study design that is being described.
a. A study examined the effect of hormone replacement therapy on cancer; cancer cases were identified by using a cancer registry in northern California. Controls were selected from a random sample of Bay Area cities.
b. Data from the Behavioral Risk Factor Survey were used in a secondary data analysis to examine the effect of income inequality and race on preventive health practices.
c. The level of unemployment was used as a measure of economic distress in Germany. Researchers examined the association between distress and general anxiety syndrome across states (e.g., Saxony) in Germany.