Why Would a Researcher Want to Insure That Every Person

Why would a researcher want to insure that every person in the larger group of study has an equal chance of being included in the sample?

A) It provides important epidemiological information such as the prevalence and incidence of the disorder.
B) This helps eliminate a correlational relationship.
C) It increases the chances of finding a causal relationship.
D) It increases the researcher's ability to generalize findings to the larger group.