sampling

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sampling

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 ?
Because the data is being sampled and the detection mechanism is typically a threshold, the sample data must be scaled in relation to the sample rate used by the data source.
Contrary to the belief that sampling at a rate higher than the natural frequency of the pulsation will reduce meter error, the factory default sample rate of 10 SPS produced the best results for all tests.
The sample width is 600 ps for the sampler and store, and remains fixed for all sample rates.
Digital audio can be routed from the receiver output or a standard serial audio port into the stereo asynchronous sample rate converter.
This produces a band of information which, when reconstructed, produces an infinite number of replicas of that information mirrored at half sample rate intervals.
The AWG70000A Series meets this need with an industry-leading combination of 50 GS/s sample rate performance, 16 GS of waveform memory and 10 bit vertical resolution.
Typically, these lower bandwidth models thus have excess sample rate versus what would be needed to reconstruct signals without aliasing.
Other machines use touch probes that bounce over the surface of the tire as it spins, creating errors or low end laser sensors that do not perform as well as the high end lasers with high sample rates and sophisticated light control circuits.
Our flagship Q5 Sample Rate Converter allows the platform to act as a digital audio hub, preserving audio quality and unifying the multitude of sources in today's multimedia systems, not a commonly found feature in this market space.
TAS5548 and TAS5558 are HD-compatible pulse width modulators with digital audio processing and sample rate converters.
WaveAce 1000 oscilloscopes feature a sample rate of up to 1 GS/s with 2 Mpts of memory in two-channel models from 40 MHz to 100 MHz.
For tire uniformity machines, the Optocator has a sample rate of 16 kHz.