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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
References in periodicals archive ?
When the single update PWM is used, system response to unit step change with the resistance r changing is shown in Figure 9, while the sampling frequency [f.sub.s]=10kHz and [k.sub.at_critical]=0.5 are constant.
Since several existing algorithms achieve high-precision measurements at the expense of low energy efficiency, we developed a proprietary algorithm which is able to adapt sampling frequency by performing flexible sleeping periods which does not affect the quality of measurements.
After the enhancing the audibility process of G.722, the signal is again converted into 16 bit format with the sampling frequency of 44.1 kHz as shown in the figure 10 since the AAC codec accepts only of these formats.
The conversion time of the ADC is 10 ns at a sampling frequency of 100 MHz, realizing an integration time of 48 [micro]s for the full size sensor.
which means that a unique mapping is still possible, yet only if the bandwidth [DELTA]f is not larger than the sampling frequency. In addition to this, the frequency range must be known.
Higher frequency terms also are created by the resampling but are removed by a low-pass filter at the 75-GHz sampling frequency.
As per the sampling theorem, in order to make a discrete time-series signal sampled reproduce the original input signal without distortion, the sampling frequency must be at least twice the highest frequency of the input signal; otherwise frequencies will be confusing or wrong.
For the data transmission stage, the sampling frequency that must be used for functional requirements is 2KHz, which means that every 0.5ms data are being sent.
sampling frequency should be greater than twice of the analog signal frequency (Shannon Nyquist Criteria) [1].
(1) Sampling frequency: the number of times per second at which analog audio is sampled to digitize its waveform.