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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.
Collins Dictionary of Business, 3rd ed. © 2002, 2005 C Pass, B Lowes, A Pendleton, L Chadwick, D O’Reilly and M Afferson
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(Full citations are available at We measured value-added with the average change in combined reading and math scores for a school's students between the end of 3rd grade and the end of 4th grade; we measured cross-cohort changes with the change in 4th grade scores from one year to the next, Among median-size schools in North Carolina, roughly half of the variance between schools in value-added in 4th grade math and reading was due to sampling variation and other one-time factors.
[TABULAR DATA FOR TABLE 4 OMITTED] Our interpretation of the negative temporal variance estimates is that the temporal variation is close to zero, or that the sampling variation is relatively large in comparison to the true temporal variability, and thus difficult to estimate.
Bulmer's R test.--With no sampling variation, Type I error rates for Bulmer's R test were not different from the set nominal value of 5% for all time series lengths and all magnitudes of process variation (Fig.
Because the coefficients in these functions are estimated, the functions exhibit sampling variation and the confidence intervals for the estimated values of the function allow the researcher to make determinations regarding clinical or policy significance of the estimate.
The researcher will get the same value, apart from random sampling variation, in the validity study.
Studies are currently underway to examine additional means of reducing sampling variation and to address the sensitivity of the measurement to ambient conditions.
Sub-sampling 2000 times was used in this and subsequent analyses since this sample number was sufficiently greater than that number where sampling variation becomes relatively unimportant.
Consequently, the extremes in a collection of parameter estimates are liable to be of little value in identifying extremes among the actual parameters; the true ordering can be masked by sampling variation.
However, if the data [v.sub.rt] are contaminated by outliers, these least-squares estimates are unduly susceptible to sampling variation and may be quite unstable.
This approach isolates the sampling variation from the parameter variation, which for most PSAs is controlled by the selection of the variables and the range of variation selected by the modeler.
*** That is, you assume the differences in the effect between studies are due only to sampling variation.
For an elementary school of average size in North Carolina, it is estimated that 28% of the variance in fifth-grade reading scores results from sampling variation and about 10% results from other nonpersistent sources.