# 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 ?
The autocorrelation functions of speech and voiceband data signals have approximate values of 0.85 and 0.2, respectively, for the waveform sampling at 8000 samples/sec, which is the sampling rate of standard ADPCM. On the other hand, the frequency domain characteristics of speech and voiceband data signals can be illustrated by comparing their spectra.
Then, an ADPCM system should be used, where the adaptation of the coefficient of the predictor to the changes of the correlation coefficient [rho] is done during the time.
Thus one is led to ADPCM data compression, quickly becoming a standard on most cards.
11, we implement another DVFS-based reliability-aware energy efficiency method RA-DPM [19], and perform comparison with our proposed method on adpcm, fft1k and matmul programs.
With AuriStream, CSR has introduced Adaptive Differential Pulse Code Modulation (ADPCM) as an enhanced voice coding method, since ADPCM scans at 32 Kbps, CVSD 64 Kbps for Bluetooth power savings in the handset.
ISO/MPEG 1 layer two at 48 Ksps and 16 bits sampling HI-FI, single channel at 128 Kbps HI-FI, two channels, 64 Kbps each Voice: ADPCM 32 Kbs
Several access modes are competing for industry standard: the front runner is TDMA (time division multiple access), which digitizes voice signals (similar to PCM and ADPCM) and interleaves multiple conversations over individual frequencies.