A convenience sample is a study of subjects taken from a group that is conveniently accessible to a researcher. One advantage of this is that it is easy to access, requiring little effort and time. This sampling method suffers from a major disadvantage in that it is not an accurate representation of the population, which can skew results quite radically. Use of a convenience sample is quite popular and prevalent, however, and it can be valid under certain conditions.
One frequent setting for a convenience sample is a college or university. Sociology students, for example, may want to conduct a survey to learn more about a particular issue, such as certain beliefs regarding social background and income. The students might distribute the survey to their classmates, because the members of the class are easy to access and the researchers are likely to get a high response rate. This sample is "convenient" because it is readily available to the students conducting the survey.
In general, the major advantage to a convenience sample is the availability of such a population. Researchers choose this type of group to gain information without having to travel extensively or build a pool of wide-ranging subjects. This often saves both time and money, which can make a tremendous difference while performing research.
Biases and Flaws
Any number of biases can occur in a convenience sample. By selecting from a specific population such as students enrolled in Sociology 101, people visiting a mall between 10:00 am and 2:00 pm on Saturdays, or library patrons, the study inadvertently excludes a great deal of the population. Choosing only students in a particular classroom at a certain university can easily exclude certain portions of the general populace, such as children or those without the financial means to attend the school.
Such exclusions are not always a problem. For example, a study on library patrons could easily take a convenience sample of people at a certain library and generalize the results. On the other hand, a study on social attitudes toward people with disabilities should not use only the students in a sociology class, which does not necessarily represent an accurate cross-section of the population. This inability to accurately generalize the results of such a group makes it ineffective for many studies.
Other Sampling Methods
Researchers who want more valid results typically take a "probability sample," which attempts to get an accurate representation of the population. It is not generally possible to study everyone, but it is possible to randomly assign people to a study with an eye toward retaining a balance of characteristics seen in the population in general. For example, organizations that conduct political polling usually try to draw on a large database of people and select subjects randomly. This randomization increases the chances of a more accurate pool forming to produce results that can be better generalized.
If a convenience sample is used, researchers typically disclose this fact. Good research usually includes a detailed overview of the sampling techniques used, so that people reading about it have a better understanding of how it was conducted. When revealing that a convenience sample was used, the researcher may also present justifications for its use and defend its accuracy.