biased sample


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biased sample

[¦bī·əst ′sam·pəl]
(statistics)
A sample obtained by a procedure that incorporates a systematic error introduced by taking items from a wrong population or by favoring some elements of a population.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

biased sample

a population SAMPLE which is not a true reflection of the parent population (see BIAS 2), i.e. not a REPRESENTATIVE SAMPLE.

When the incidence of a certain occurrence or piece of behaviour in a population is to be investigated, e.g. voting intention, it is often impossible to examine the total population, so a sample of this population is taken. For this sample to produce acceptable data, it must be a true representation of the parent population, so it is essential that it is selected in a way that ensures this. If this is not managed, bias will result and the information collected will not truly reflect the population being studied. Thus, to select a sample by questioning people in the street will bias it against people who do not walk, do not go shopping, are at work or school all day Postal QUESTIONNAIRES attempt to overcome this type of bias, but are likely to be biased against those who do not bother to fill in questionnaires and re turn them, and against the illiterate. To keep bias to a minimum, if random sampling is not possible, it is necessary to select the sample carefully by matching all relevant parameters of the population, e.g. age, class, residence, etc, and to ensure as high a response rate as possible, probably by personal INTERVIEWS.

Collins Dictionary of Sociology, 3rd ed. © HarperCollins Publishers 2000
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Biased Sample: Estimation by Incorporating Information in the Predictor Variable Importance Weights.
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Summaries of evidence will yield misleading results if they try to combine results across patient groups or test methods that are too heterogeneous; if they assemble an incomplete, biased sample of potentially available studies; or if they use results from studies that are themselves methodologically weak and very susceptible to bias.
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ONCE again, the Looking Back picture storms to the top of most popular item chart in the Daily Post, our statistics being based on a totally biased sample derived from Trust the Post's bulging mailbag.
A conservative organization, the Colorado-based Physicians Resource Council, told the AAP that the studies on which the academy based its decision had inadequate sample sizes, biased sample selection, lack of proper controls, or failed to account for confounding variables.
Admittedly, our survey is a small and somewhat biased sample. Nonetheless, the findings contain some important messages.
But, they state, the search engines "typically index a biased sample of the Web." They point to the overemphasis on popular pages, or pages with many links, and suggest that valuable new research is not found by the researcher who needs it because of this propensity.
In this note, we show that the DWS is a severely biased sample of workers who have lost their jobs.(6) By pooling the DWSs, it is possible to compare estimates of the number of displaced workers for the same point in time based on recollections from different points in time.