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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 ?
If instead Y is a bounded convex spatial set containing O, the volume and the surface area of Y may be estimated by a two-step procedure which involves circular systematic sampling in a section through O and the use of the cubed radial function or the squared support function (Gundersen, 988; Cruz-Orive, 2005).
While systematic sampling may seem convenient, it can pose problems when there is a systematic pattern associated with how the data were sorted.
The program calls for systematic sampling of meat cuts at the retail level and comparing the DNA with that of source animals.
Systematic sampling, or grid sampling, ensures that the entire site is represented by individual samples.
A systematic sampling technique was employed to select 10 percent of delinquency cases petitioned to the Los Angeles County Juvenile Court by the LAPD in 1940 (cases petitioned by other agencies, such as the county sheriff's office or probation department, were excluded, as were dependency cases--LAPD-initiated cases involving neglect and abuse).
Systematic sampling was the most efficient sampling scheme over the observed range of occupancy rates (Table 2) because fewer boxes would be required to achieve desired levels of precision compared to stratified random sampling.
Participating countries decided to obtain information on forest conditions through a common monitoring system in two intensity stages:- Extensive monitoring on a systematic sampling network includes the annual assessment of the crown condition of trees, their nutrition and the forest soil condition on an extensive scale.
Many ecologists use two-dimensional systematic sampling to estimate mean density of individuals over the domain sampled.
If the variable or attribute is approximately evenly divided among members of the population, then we have a homogeneous population and we can use a simple sample design such as random or systematic sampling.
The county and diocesan archives take a back seat to the testamentary as it is her systematic sampling of more than 3,500 wills that forms the archival backbone of this monograph, the results of which are contained in an appendix of tables and graphs.
However, systematic sampling requires that the random numbers be assigned to the invoices.
Regarding the past, International Atomic Energy Agency (IAEA) experts believed that systematic sampling and careful segregation of rods from particular parts of the reactor's core under its supervision would disclose how long the fuel had been burned and at what intensity.

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