StATS: What is a quota sample?
A quota sample is a convenience sample with an effort made to insure a certain distribution of demographic variables. Subjects are recruited as they arrive and the researcher will assign them to demographic groups based on variables like age and sex. When the quota for a given demographic group is filled, the researcher will stop recruiting subjects from that particular group.
I've seen quota sampling used in a shopping mall. A researcher carrying a clipboard will come up and ask every passerby to participate in a survey. After a while, they let certain people walk by but still try to stop people in the demographic groups that have not yet filled their quota. It seems like my demographic group (male aged 40-50) is one of the last groups to be filled, because men tend to avoid shopping malls and they have a greater mistrust of researchers carrying clip boards.
I've also been part of several telephone survey which appear to be quota samples, but here I seem to be on the opposite end. When they find out how old I am, they stop asking questions, because I'm part of a demographic group whose quota has already been filled.
A quota sample insures balance across a small number of demographic factors, but still has many of the same problems of a convenience sample.
Further reading
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