Which of the following is a case-control study?
a. Study of past mortality or morbidity trends to permit estimates of the occurrence of disease in the future
b. Analysis of previous research in different places and under different circumstances to permit the establishment of hypotheses based on cumulative knowledge of all known factors
c. Obtaining histories and other information from a group of known cases and from a comparison group to determine the relative frequency of a characteristic or exposure under study
d. Study of the incidence of cancer in men who have quit smoking
e. Both a and c
Answer: c. Obtaining histories and other information from a group of known cases and from a comparison group to determine the relative frequency of a characteristic or exposure under study