Relying on available subjects, however, is extremely risky and comes with many cautions. For example, this method does not allow the researcher to have any control over the representativeness of the sample. That is, the researcher cannot control how well the characteristics of the sample (gender, age, race, education, etc.) match the characteristics of the larger population it is intended to represent.
Convenience sampling is typically only justified if the researcher wants to study the characteristics of people passing by the street corner at a certain point in time, for example. It can also be used if other sampling methods are not possible. The researcher must also take caution to not use results from a convenience sample to generalize to a wider population.
Let’s say that a researcher and professor at a University is interested in studying drinking behaviors among college students. The professor teaches a sociology 101 class to mostly college freshmen and decides to use his or her class as the study sample. He or she passes out surveys during class for the students to complete and hand in.
This would be an example of a convenience sample because the researcher is simply using subjects that are convenient and readily available. This sample would not be representative of all college students and therefore the researcher would not be able to generalize his or her findings to all college students. The students enrolled in the sociology 101 class, for example, could be heavily weighted toward a certain characteristic (mostly freshmen, for instance).
While the results of this study could not be generalized to the larger college student population, the results of the survey could still be useful. For example, the professor could use the results to refine certain questions on the survey or come up with more questions to include on a later survey. Convenience samples are often used for this purpose: to test certain questions and see what kind of responses arise and use those results as a springboard to create a more thorough and useful questionnaire.
Babbie, E. (2001). The Practice of Social Research: 9th Edition. Belmont, CA: Wadsworth Thomson.