Quota sampling

The quota sample ( quota sample) is a special systematic sample.

Quota samples are not random samples, but are based on a conscious choice of the target population. In a quota sample is attempted, a representative composition of the sample by setting quotas on certain characteristics, their distribution in the population must be known to bring about. The interviewers will be made ​​precise specifications which properties need to have the persons to be interviewed.

The quality of a quota sample can be checked by the distribution is not quoted, but is compared to the population of known characteristics in sample and population statistics. Were the characteristics of age, gender and place of residence size used, for example, a quota sample based on census data, the additional feature can be used denomination, to determine the extent to which the sample of the population corresponds.

Application

Quota samples are used in the social sciences and especially in psychology. One reason for the application of the quota sample in survey research is the low response rates in random sampling, which now lie in telephone surveys in the U.S. in the single digits. In a quota sample interview objectors are replaced by so-called Statistical twins, who have the same ratio features. This is based on the assumption that statistical twins are also similar in the unquoted characteristics ( see above). In this way, there are at quota samples no (visible) sample loss, which can distort the results of random samples to a considerable extent.

Scientific debate on the quota sample

The science and the benefit of quota samples are controversially discussed in social science for decades.

Critics and opponents of the method base their rejection on several arguments. The first argument is that the mathematics of a random sample based on quota samples is not applicable. Thus, it is also not allowed ( but nevertheless technically possible ) to calculate indicators for the quality of a study, including confidence intervals. Another argument is the influence of the quality of the interviewers working on the result: the selection of specific target person is left to the interviewer in the quota sample. Through this procedure, the interviewer get a big influence on the course of the study. Only when they work correctly, the sample corresponds to the quality criteria. Since the interviewers are paid per guided by interview and there is a follow-up difficult because of the protection of the anonymity of the respondents, quota samples are prone to manipulation. In addition, the method includes the selection probability for easily accessible persons increases or out, just reached the quota sample people that just will not let that question, as with a random sample.

Users and advocates of the quota sample, however, argue with the results in research practice that are at least as good as the obtained with random sampling. Given the declining response rates in random samples should also improve the representativeness shall be sought through renunciation of random sampling.

Quota samples are subject to certain conditions and faster - however, depending on the survey mode ( telephone, in person, by mail, online) - more efficient than random sampling. This is especially true if there is no list to be interviewed people exists from which a random sample could be drawn. Due to the quota requirements also the discretion of the interviewer will so severely restricted that a random sample will approximate.