sampling

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sampling

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 ?
Because of this, a nonprobability sampling (purposive sampling) method was used in the process of gathering data from the respondents of both universities.
A nonprobability sampling, using a purposive sampling technique was used to collect data.
Processes of probability and nonprobability sampling are discussed in a lucid manner.
Nonprobability sampling was used to select members of the control group, because each participant was selected with respect to matching the demographic characteristics of the treatment group.
However, the use of a nonprobability sampling methodology precludes generalization of the results beyond the present respondents.
Consequently, nonprobability sampling was utilized in the present report.].
We chose the nonprobability sampling technique of convenience sampling.
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.