Answer :
Final answer:
The study conducted to investigate if potato salad caused a food-borne illness outbreak by interviewing both affected and unaffected individuals is a case-control study, which compares exposures between cases and controls.So the correct answer is A. case-control.
Explanation:
In the given scenario, where the goal is to determine if potato salad served at a local farmer's market a month ago caused an outbreak of a food-borne illness, and individuals who had eaten potato salad and developed the illness as well as those who did not develop the illness were interviewed, the type of study conducted is a case-control study. In a case-control study, individuals who have the disease (cases) are compared with individuals who do not have the disease (controls) to see if there was a difference in exposure to a suspected risk factor. This type of study is particularly effective in investigating outbreaks and identifying potential sources of such outbreaks, allowing for efficient data collection and rapid analysis.