sampling (statistics)

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In statistics, taking a small number of cases and assuming that they are representative of the total number. In survey work in market research, for example, it is usually not practical to survey every customer. It is also important in quality control to avoid the expense of testing every item produced. Instead, a sample is taken. A random sample is one where the sample is chosen in a random way.

For example, in a postal survey, one person in every hundred on the electoral register might be chosen. A stratified random sample is one where a group is selected and then a random sample is taken from that group. For example, a manufacturer of baby-care products might select pregnant mothers as a group, and then conduct a random-sample survey on that group. A quota sample survey is one where the size and composition of the survey matches the total population that is being researched. For example, a psychologist may want to interview 20 boys aged 0–10, 20 girls aged 0–10, 20 males aged 10–20, and so on.

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