Convenience Sampling

Convenience sampling is a type of survey sampling in which interviewers are allowed to choose convenient members of the population to interview. The goal of a survey is to gather data in order to describe the characteristics of a population. A population consists of units, or elements, which, depending on the application, can be individuals, households, land areas, bank accounts, or hospital records at a specific time and location. A survey collects information on a sample, or subset, of the population. In some surveys, specific units or elements are chosen by the survey designers to be in the sample. Interviewers are assigned to interview the members of the selected sample. Sometimes multiple attempts at contacting and collecting data from the selected sample members are made. In convenience samples, on the other hand, interviewers themselves are given some latitude in selecting the population members to interview. That is, the survey designers and planners do not strictly control the selection of the sample.

Convenience samples occur in many forms. If an interviewer is told to stand on a corner or at the exit of a shopping mall and find adults to complete a survey about local schools, then this is a convenience sample because the instructions of whom to interview are not explicit. If customer satisfaction forms are distributed to certain customers in a restaurant, then this is a convenience sample if the waiters are allowed to choose[Page 187] which customers to give comment forms. Internet and call-in opinion polls also could be considered convenience samples in which the sample essentially selects itself by choosing to participate. A subtler example of convenience sampling occurs when a telephone interviewer dials the telephone numbers that are randomly generated from a computer until a willing respondent is found. Although the telephone numbers are being provided to the interviewer, the interviewer is going to speak to the first available and willing people reached. This is a convenience sample because the survey planners are not picking specific numbers that should be called. In this scenario, the people called by the interviewer essentially decide themselves whether or not to be in the sample.

In the shopping mall example, it is likely that the interviewer will tend to approach people who look friendly and are walking at a casual pace rather than people who are rushing and in a visibly bad mood. Interviewers might tend to choose people of their own gender, age group, ethnicity, or race to interview slightly more often than they choose others. The interviewer also is likely to choose a desirable place to stand and to avoid loud places, such as by the door to a video arcade, and smelly locations, such as near a garbage or designated smoking area. As a result of the chosen location and tendencies to approach certain types of individuals and avoid others, it is possible that the convenience sample will not produce results that are truly representative of the entire population of interest. The convenience sample could be representative of certain subgroups in the population, but due to the lack of control by the survey planners, it is difficult to specify which population exactly is being represented.

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