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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 ?
Sample comprised of 200 left behind wives of overseas migrants of Sudhanotti and Poonch district of AJandK, and was selected by using non probability purposive sampling technique.
Diagnosed CP children of age 12-14 years were sampled by non-probability purposive sampling from the Cerebral Palsy Clinic.
This study was conducted on 30 Jan 2016 during the pre and post workshop sessions in order to explore the teacher's motivation through faculty's perspective at the Army Medical College, using non-probability purposive sampling technique.
Sample was collected through purposive sampling technique from different universities of Karachi, Pakistan.
The sampling technique was non probability purposive sampling.
Using non-probability purposive sampling, all mammograms in the study were interpreted by three radiologists on the basis of Breast Imaging Reporting and Data System categories and by assessing the breast density composition.
Through purposive sampling techniques, 21 students from 6 different online graduate courses in the College of Education were selected as participants.
Material and Methods: Three hundred and sixty six illiterate and employed married women in the reproductive age group were approached using non probability purposive sampling.
They was selected on the basis of purposive sampling and were then categorised into two equal groups of 'acute' and 'non-acute' respiratory infection.
Material and Methods: Purposive sampling was done and consisted of seventeen teaching faculty members of undergraduate subjects and two qualified medical educationists.
Methods: The retrospective study, with purposive sampling of the patients of acute cholecystits in age above 18 years, who were operated within 10 days of onset of symptoms, was conducted at the Department of Surgery, Dow University Hospital, Karachi, by reviewing the patients' medical record from March 2010 to August 2012.