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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 ?
729 speech codec for the development of their next generation VoIP enabled products," stated Larry Przywara, Tensilica's director of mobile multimedia products.
Moreover, we compare performance of the proposed schemes with the wideband rate distortion bound, which represents the lower bound of performance of several standardized ADPCM speech codecs for wideband speech, including the G.
862 for the Assessment of Wideband Telephone Networks and Speech Codecs, ITU Rec.
Virtual Office Desktop also incorporates echo cancellation and advanced speech codecs to improve audio quality, even with low bandwidth connections.
The text is unusual in providing a complete history of the development of the technology, followed by its detailed description of theory and practice, including an exhaustive discussion of all current standardized speech codecs.
The modules GSM voice data, fax and SMS support provide access to a TCP/IP stack via AT commands, as well as support for HR, FR, EFR and AMR speech codecs.