Frequency claims is divided into construct validity and external validity. Recall that external validity concerns both samples and settings. Population: some larger group from which a sample is drawn, which the sample is intended to represent. Sample: the group of people, animals, or cases used in the study. Census: a set of observations that contains all members of the population of interest. Before researchers can decide whether a sample is biased or unbiased, they have to specify the population to which they want to generalize. A study"s population is whatever the researchers say it is. The sample is biased when it is unrepresentative of the population. A researcher"s sample might contain too many of the most unusual people. A researcher"s sample might include only one kind of people, when the sample of interest is more varied. Sampling only those who are easy to contact. Researchers may sample groups who are convenient to contact, such as students.