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sampling

sampling

The policy of inferring the behavior of a whole batch by studying a fraction of it. [MF essample, from L. exemplum, taking out]
biological samplingdenotes sampling that can be taken without jeopardy to the whole organism (e.g., for hematological or biochemical study). Because of the complexity of biological samples it is usually supposed that the source of the sample is thoroughly mixed and hence representative; this assumption is often not true e.g., in genetic studies in mosaic patients.
chemical samplinga sample that is obtained by whatever means is convenient and then purified of irrelevant elements before analysis; the assumption of thorough mixing is not necessary.
haphazard samplingthe assembly of data in an unprescribed and undefined fashion that allows no sound scientific inferences other than establishing the existence of types. (Finding even one unicorn in such a set would establish that unicorns can exist, but no inference about their prevalence could be made from it.) Cf. random sample.
random samplinga selection of elements by a formal randomizing device for purposes of inference about a population of inference from that population in such a way that the probability of each possible outcome may be precisely specified in advance; the inferences are necessarily stochastic.
snowball samplinga method whereby interview subjects for a statistical study are obtained from subjects already interviewed for that study.This technique is most often used with target populations made up of elusive or uncooperative subjects (e.g., IV drug users). Those subjects first contacted are asked to name acquaintances, who are then approached, interviewed, and asked for additional names. In this way, a sufficient number of subjects can be accumulated to give a study adequate power.

 

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