Rather than collecting data on everyone in the targeted population, researchers often use a sample that is intended to represent the entire population. So, most studies whose population is all households in the U.S. do not actually collect data from each household in the U.S.; instead, they might use a sample of a smaller number of households that is representative (in terms of age, race, family structure, etc.) of all households in the U.S. The authors should be clear about how their sample was obtained and offer information allowing the reader to know to what extent it is representative of the population that is being studied