ABSTRACT
A population may be large, such as all social workers in the United States, or small, such as all social workers employed by a specific hospital. If a researcher studies every member of a population, the researcher is conducting a census. For large populations, however, it is more efficient to study a sample instead of conducting a census. One of the methods for selecting an unbiased sample is to give every member of a population an equal chance of being included in the sample. Volunteerism might bias a sample even if a researcher begins by identifying a random sample from an entire population. For instance, a researcher might draw a random sample of all freshmen at a college and contact them to take part in a study of attitudes toward the use of instructional technology in higher education. For a variety of reasons, many of those in the random sample the researcher has selected may refuse to participate.
