To select a random sample for a population:
1. Select members at random from the target population only.
2. Eliminate samples that do not give every member of the population an equal chance of being chosen.
Selecting every third woman entering a department store in New York does not give a random sample representing the population in Florida, since it includes members from a different target population.
Selecting every third man entering a bar or every third person entering an opera concert does not give a random sample of the entire population because not everyone has an equal chance of being selected.