Immediately after the Introduction, which includes a literature review, most researchers insert the main heading of Method or Methods. In the Method section, researchers almost always begin by describing the individuals they studied. This description is usually prefaced with one of these subheadings: Data, or Sample, or Subjects, or Participants. A population is any group in which a researcher is ultimately interested. Researchers often study only samples for the sake of efficiency, then generalize their results to the population of interest. Researchers use stratified random sampling by drawing individuals separately at random from different strata within a population. If a researcher is planning to study how psychologists work with illicit substance abusers in New York State, stratifying on geography will improve the sample if the various areas of the state tend to have different types of drug problems. Many researchers have limited resources with which to conduct research: limited time, money, and assistance.