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:

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;
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.

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References in periodicals archive

The big advantage claimed by analog processing is low power-- really low.

Moving the analog-digital boundary

Installing, configuring and maintaining IP cameras is also easier than with analog. Many IP cameras can be configured remotely using an online interface, which simplifies changes and troubleshooting.

Surveillance: Analog to IP

Philip Corby, an equipment engineering manager with Analog Devices, explained: "Our technician roles offer extensive variety and the opportunity to work on leading edge technology.

YOU CAN BE AT CUTTING EDGE; Hi-tech leaders look for new recruits to join them

The two products help reduce analog layout creation time.

Magma Design Automation Launches New Tools

"That's the nice thing about the system, and one of the reasons we chose it." Although the district bought a few wireless handsets for use out on the athletic fields and playgrounds, Stevenson notes the low-cost analog phones have enough functionality to suit every school's needs.

Roaming charges: wireless VoIP handsets are more expensive than their analog counterparts, but some districts find they're worth the cost

Temperature-indicating, controlling, and recording instrumentation includes handheld digital and analog pyrometers, infrared thermometers, thermocouple sensors, scanners and controllers.

Temperature sensors, monitors, controls

Analog data received from the camera are equivalent to 8 data bits.

Fully automatic x-ray inspection for tire manufacturers--part 1

With small-package op amp solutions, Microchip continues to expand into the portable market space, where high-precision analog is required in a space-saving form factor and at a competitive price.

Microchip Technology brings ultra-small SOT-23 package options to operational amplifier portfolio

In many cases, engineers have preconceived notions about mixed-signal designs and how analog and digital placement, partitioning and associated design should be performed.

In the mix: tips for mixed-signal design: avoiding preconceived notions is a must if you want to design efficient mixed-signal boards

Panasonic Security Systems of Secaucus, New Jersey, has introduced a series of network server solutions that allow integration of IP-addressable and conventional analog cameras, so security professionals can use advanced analog camera systems in a networked environment.

Hybrid networking solutions

Says Welsh, "We've shown that if you give [a chemical analog of 1,25-D] to an animal that already has a mammary tumor, that tumor will regress." Other researchers, she notes, have used 1,25-D analogs to inhibit the spread of cancer or the growth of blood vessels that feed new tumors in laboratory animals.

Vitamin boost: from muscle strength to immunity, scientists find new vitamin D benefits