Sampling 1 - Sampling An Introduction to Sampling Surveys...

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Sampling
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An Introduction to Sampling Surveys are usually a study of a sample of a POPULATION Typically data gathered from a SAMPLE (subset) of a population are used for the purposes of generalizing to the larger population from which the sample is drawn Gathering data from samples is more cost effective and takes less time than surveying the entire population If you were to survey of an entire population your sample would be called a CENSUS
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A SAMPLING UNIT is an individual item selected for inclusion in the sample from the population being sampled A SAMPLING FRAME is a list or system that identifies every member of a population (sampling units) Usually includes every member of a population but rarely does
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A Population A population is sometimes referred to as a UNIVERSE A population is a group of persons, institutions, or events that you are wanting to generalize from POPULATION UNITS may be households or individuals, companies or subsidiaries or plants Defining the population (universe) Must know who (what) you are interested in: persons, families, organizations, products (unit of analysis) Must know who (what products/services) is included in that population Usually a subset of a much larger population Don’t define your population too narrowly, broader is better
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Setting Population Boundaries Screening Variables (Population boundaries) include: Those factors clearly separates the population of interest from others Must be stated operationally so that those administering/selecting the sample can determine eligibility Should be relatively easy to implement (Income, Geography, Class, Attitudes, Intentions)
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Framing the Population May be difficult to acquire. A population frame is not available for the US nor for any subgroup thereof (list of minorities, women, men, etc.) However, you may obtain mailing lists which are generally constructed from membership or subscription lists. Examples of a population frame may include printed directories, such as, the telephone book, city directories, organizational list, or a computerized file generated by a sampling firm, such as Genysis or Survey Systems Inc
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To generate a population frame without a list you must construct a COUNTING FRAME Estimate the size of the population Randomly select a sample of numbers from 1 to the size of the population Count the population and collect data from the appropriately numbered units
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Problems with List and their Solutions Ineligibles Duplications Omissions Clustering
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Ineligibles Persons or companies not apart of the population Estimates of eligibility can be estimated during pretesting or they can be based on prior research If you are estimating eligible good rule of thumb is to estimate low to make sure you get a large enough sample How to deal with ineligibles Drop them from list but you CAN’T replace them with eligibles Adjust sample size to accommodate the present
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This note was uploaded on 06/11/2010 for the course SOC 481 taught by Professor Burris during the Summer '09 term at University of Illinois at Urbana–Champaign.

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Sampling 1 - Sampling An Introduction to Sampling Surveys...

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