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 ?
As for equitability, two sampling units upstream of the artificial dam (P1 and P3), which showed higher values in the index,also had the smallest richness values, with only three species each (Astyanax bockmanni, Astyanax sp.
Shokwe Pan: The floristic association with habitat types for Shokwe Pan produced a classification (Table 6) comprising 25 plant species found in two distinct Habitat Types (Habitat Types 1 and 4) with one anomalous sampling unit (number 20) classified as a FT but in fact is a grassed floodplain occurring on the western edge of Shokwe Pan and as such constitutes an outlier in this classification.
Again, as long as there is no double counting on the list of expenditures, sampling units can be grouped, sliced, diced, paired, or listed in any convenient manner for sampling.
On average, the primary sampling unit in which women lived was seven kilometers from the nearest health facility offering delivery care.
Hence, systematic scanning of one sampling unit took about one hour with each method, making the comparison of precision realistic.
Two sampling units were randomly selected and extracted quarterly from Stacy Creek starting July 2004.
The sampling units might be physical items (for example, checks listed on deposit slips, credit entries on bank statements, sales invoices, or accounts receivable) or monetary units.
As a sampling unit, a sycamore leaf can contain hundreds of aphids, though counts are commonly much lower.
In situations where auxiliary biological information provides a pre-assignment of some catch individuals into a priori sampling units, each known to represent a single unknown origin, the above formula still applies.
Self-representing: A term applied to primary sampling units that are selected with certainty into the sample, usually because of their size.
8% of the sampling units along the transects compared to a mean area of 14.