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the selection of part of a total population of consumers or products whose behaviour or performance can be analysed, in order to make inferences about the behaviour or performance of the total population, without the difficulty and expense of undertaking a complete census of the whole population.

Samples may be chosen randomly, with every consumer or product in the population having an equal chance of being included. Random samples are most commonly used by firms in QUALITY CONTROL where they are used as a basis for selecting products, components or materials for quality testing.

Alternatively, samples may be chosen by dividing up the total population into a number of distinct sub-groups or strata, then selecting a proportionate number of consumers or products from each sub-group since this is quicker and cheaper than random sampling. In MARKETING RESEARCH and opinion polling, quota sampling is usually employed where interviewers select the particular consumers to be interviewed, choosing the numbers of these consumers in proportion to their occurrence in the total population.

Samples may be:

  1. cross-sectional, where sample observations are collected at a particular point in time, for example data on company sales and the incomes of consumers in the current year, embracing a wide range of different income groups, as a basis for investigating the relationship between sales and income;
  2. longitudinal, where sample observations are collected over a number of time periods, for example data on changes in company sales over a number of years and changes in consumer incomes over the same time periods, as a basis for investigating the relationship between sales and income. See STATISTICAL INFERENCES, QUESTIONNAIRE.
References in periodicals archive ?
Intentionally, the sampling method used was purposive nonprobability sampling, an appropriate method for testing theory.
Therefore, a nonprobability sampling was appropriate for this study.
Within the preview of nonprobability sampling strategies, the use of diverse participants can enhance the validity of the results by mitigating various biases (Babbie, 2007).
To select the participants, the most common form of the nonprobability sampling approach--purposive and convenience sampling techniques were used.
We recruited 18 subjects with diabetic foot ulcers by performing simple nonprobability sampling and approaching the consultant physician.
The weakness of all nonprobability sampling is its subjectivity that precludes the development of a theoretical framework for it.
Although the results of this survey may not be generalizable to all nursing personnel because of the nonprobability sampling method and inclusion of only RNs, the results suggest that concern over safety may be contributing to hospital personnel shortages and hindering recruitment efforts.
Students should be warned of the inherent dangers of subjectivity and bias associated with nonprobability sampling techniques, in addition to the comment that the 'criteria for sampling must be explicit and systematic'.
For this study, a nonprobability sampling technique (purposive sample) was used to conduct a self-administered survey to Dauphin County Adult Probation and Parole officers after obtaining permission from the DCAPP director or chief adult probation officer.