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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 ?
The 2010 dataset was obtained by sampling soils according to a stratified random sampling scheme so the mean SOC and associated variance for each SLU complex could be estimated using design-based approaches (de Gruijter et al.
You might be wondering, "If stratified random sampling improves the accuracy of inferences, why isn't it done more often?
Because LQAS is based on stratified random sampling, results from lot samples can be combined to obtain a point estimate for the entire population, allowing for a small sample size.
Additional aliquots from six bottles of RM 8504, selected according to a stratified random sampling scheme, were analyzed by GC-ECD equipped with not only a DB-5 capillary column (described above) but also one with a relatively non-polar stationary phase (DB-XLB, J & W Scientific, Folsom, CA).
More recently, dredge stock assessments have been supplemented by annual patent tong surveys based on a stratified random sampling design.
practice of stratified random sampling and tenfold cross-validation, we
Sampling stations were selected using a stratified random sampling design.
Stratified random sampling was also used in order to secure equal numbers of males and females in both settings.