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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 ?
The next component consists of a cascade of filters to filter and to downsample each microphone signal.
Therefore, before implementing the VTR, we need to downsample [chi] using an appropriate sample factor [rho].
Because the horses in the dataset have almost the same size, we randomly choose the sampling ratio to upsample or downsample all the images (and the corresponding label maps) in the dataset to create a new dataset, in which large scale-change of objects exists.
Yet another encoding alternative is to downsample (subsample) the left and right views to fit into one frame of the original video resolution.
Here nonuniform means downsample rate of channels are different not unique for all channels.
Downsample the coarse-resolution fraction images and "super-coarse-resolution fraction images" can be obtained, on which a C x C local window is used to operate to describe the super-coarse-resolution fraction block.
In order to ensure efficient and effective performance of the proposed method, a preprocessing step that downsample the high-precision face data is needed in our experiment.
Once we find this optimum tradeoff, we can adjust the camera setting or downsample the input data.
After implementing the optimizations described in section 4, we concluded that the best practice to obtain the lower error in the shorter time is to downsample the picture and to reduce the points, only keeping the middle of each entity.