Whereas, with a nonprobability sample, you cannot indicate the probability of an individual or unit being selected. Two types of nonprobabilistic samples are convenience and quota sampling. Convenience sampling is simply selecting the nearest or most convenient respondents. An example of convenience sampling would be to stand on a street corner and ask pedestrians as they walk by to respond. Quota sampling is when an interviewer is given a quota of a certain type of individual to interview.
Probability sampling is, by far, the preferred method.
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