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 ?
While quantitative researchers use complex mathematical formulae to make sample size considerations, and they promote the use of random sampling (even though the overwhelming majority of studies utilize non-random samples), sample size considerations in qualitative studies are neither mathematical nor systematic.
2004-29 allows the use of statistical sampling, an analysis of de minimis fringe benefits cannot be accomplished solely through that method.
Revenue procedure 2004-29 not only permits the use of statistics, but also explains sampling standards.
Sampling Provisions of the M&E Revenue Procedure
In addition to variability in the population, the sample design and sample size also determine the amount of sampling error.
The reactor sampling device is a scaled-down version of existing flash-chamber technology, which is used for normal product removal from the continuous reactor process.
Additional chip samples collected to the south of the bulk sampling contained anomalous values up to 4.
Several companies make diagnostic kits for influenza A and B; although these tests have certain disadvantages (limited sensitivity and specificity of immunoassays), their underlying technologies can form the basis for improved influenza screening and sampling devices (2).
More thorough sampling is needed to establish fluxes of estrogens, possible uptake and accumulation, and physiological responses of marine organisms.
The memorandum proposes that through the use of statistical sampling, an estimate generated from analyzing only a portion of a taxpayer's M&E account may be used to project the expected amount of incorrect bookings made to a large M&E account.
The IRS has used statistical sampling as an audit tool for many years.
Despite an overwhelming consensus among statisticians favoring the use of sampling to improve the accuracy of the census, the bureau's proposal has proved highly controversial in Congress.