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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 ?
Obstetricians use various methods to attain fetal cells for diagnosis, including chorionic villus sampling (CVS), amniocentesis (AC), and cordocentesis (CC).
Beta-thalassemia-institution based analysis of ethnic and geographic distribution, effect of consanguinity and safety of chorionic villus sampling as a diagnostic, tool for pre-natal diagnosis in selected patients.
9) Despite the decrease in HIV transmission with antiretroviral cover, procedures that require more technical skills--such as chorionic villus sampling and cordocentesis--should still be avoided in the HIV-infected woman, as the risk of transmission to the fetus may be considerably increased.
All of these pregnant women are then offered the option of further, invasive tests including amniocentesis or chorionic villus sampling, which have about a 1% risk of miscarriage.
The risk of miscarriage following genetic Amniocentesis and Chorionic Villus Sampling was investigated in randomized clinical trials in the 1980's and early 1990's13,14.
Accuracy of cytogenetic findings on chorionic villus sampling (CVS) -- diagnostic consequences of CVS mosaicism and non-mosaic discrepancy in centres contributing to EUCROMIC 1986-1992.
Amniocentesis is associated with a one-in-two hundred incidence, and chorionic villus sampling with a one-in-one hundred incidence of abortion of the unborn child.
The ACOG guidelines also recommend that women found to have increased risk of aneuploidy based on this screening should be offered genetic counseling and the option of chorionic villus sampling (CVS) or second-trimester amniocentesis.
Both amniocentesis and another procedure called chorionic villus sampling, in which doctors pluck bits of the placenta, isolate fetal cells that can reveal many genetic problems in an unborn baby with near certainty.
Previously, the only way to know if a woman was having a baby with Down's was with second-trimester blood tests and/or invasive amniocentesis or chorionic villus sampling (CVS) tests, all of which carry a slight risk of miscarriage.
The test is not diagnostic and a positive result is usually followed up with a diagnostic amniocentesis or chorionic villus sampling test.