How Are Risk Factors for a Diseased Condition Assessed in a Population

How are risk factors for a diseased condition assessed in a population?

A) You use interviews to determine how people feel certain risk factors alter their heath.
B) You use statistical analysis of large population samples to determine correlations of risk factors with the diseased condition.
C) You cannot assess risk factors in a population because this is ultimately guess work.
D) You must choose a population to study that does not have the risk factors.
E) You must do studies on a case-by-case basis because you cannot consider general trends in a population when looking at an individual.