Editing Quota sampling (section)

==Process==
In quota sampling, a population is first segmented into [[mutually exclusive]] sub-groups, just as in [[stratified sampling]]. Then judgment is used to select the subjects or units from each segment based on a specified proportion. For example, an interviewer may be told to sample 200 females and 300 males between the age of 45 and 60. This means that individuals can put a demand on who they want to sample (targeting).

This second step makes the technique non-probability sampling. In quota sampling, there is non-[[random sample]] selection and this can be [[Reliability (statistics)|unreliable]]. For example, interviewers might be tempted to interview those people in the street who look most helpful, or may choose to use [[accidental sampling]] to question those closest to them, to save time. The problem is these samples may be [[bias (statistics)|biased]] in a way that is difficult to quantify or adjust for. For example, if interviewers decide to question the first person they see, they may oversample tall respondents (who are more easily visible from a distance), which could lead to an [[height discrimination|overestimate of average income]]. This non-random element is a source of uncertainty about the nature of the actual sample.<ref>[http://www.fao.org/docrep/W3241E/w3241e08.htm#quota%20sampling Marketing Research and Information Systems. (Marketing and Agribusiness Texts – 4)]</ref>