Researchers try to use a sample of the population that is truly representative of the people in whom they are interestedone of the main reasons for using random selection. Even so, the sample is usually selected from within a particular segment of the social world in which the researchers themselves live and work.

For example, in the United States there are some fairly distinct differences between people from the Northeast and people from the Southeast, and the same can be true in many other countries. There are also differences between large city populations and populations living in the countryside.

If a psychologist is conducting a study in a particular geographical area of a country, how might regional differences impact the study's results? What measures could or should the psychologist take to minimize the impact?