# 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 ?
In simple random sampling, every element in the population available for sampling has an equal probability of being selected.
Random sampling - a random sample of size n is selected from the combined strata.
The method of random digit dialling was used for simple random sampling.
The first section of this column reviews several standard algorithms for random sampling.
We completed in-depth surveys with wireless sales associates in the independent agent channel using stratified random sampling to represent the indirect wireless retail channel in the United States.
But a random sampling of 500 signatures proved inconclusive, forcing the Registrar's Office to check each signature for validity, he said.
Joel Schwartz at the Hazard School of Public Health in Boston examined the relationship between blood pressure and lead based on measurements of each by the Public health Service in its random sampling of U.
The surveys will be conducted every Monday, and the results from this national random sampling of Americans will be available on Tuesdays.
According to the 50-page report, a random sampling of 29 of the county's 476 group homes revealed these problems in many of these facilities that house six or more children.
But this is the first time that researchers have looked at a random sampling of births (more than 50,000 of them, at 12 hospitals) to see if the apparent associations hold up.

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