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What is a Population?

What is a Population?. The totality of cases that conform to some designated specifications The entire body of units of interest to researchers studying some phenomenon Ex: In studying the MSU student body, the population contains all students currently enrolled in classes at MSU.

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What is a Population?

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  1. What is a Population? • The totality of cases that conform to some designated specifications • The entire body of units of interest to researchers studying some phenomenon • Ex: In studying the MSU student body, the population contains all students currently enrolled in classes at MSU

  2. Census vs. Sample • Census: a complete canvass of a population; collecting information from all elements in the population • Ex: the U.S. Census • Sample: selection of a subset of elements from a larger group of objects; selecting a fraction of the population • Used most often by marketing researchers

  3. Sampling Frame • A list of sampling units (population units) from which a sample will be drawn • Could be people, institutions, geographic units, markets, households, businesses, etc.

  4. Six-Step Procedure for Drawing a Sample Define the Target Population Step 1 Identify the Sampling Frame Step 2 Select a Sampling Procedure Step 3 Determine the Sample Size Step 4 Select the Sample Elements Step 5 Collect the Data from the Designated Elements Step 6

  5. Classification of Sampling Techniques Sampling Designs Nonprobability Samples Convenience Judgment Quota Probability Samples Simple Random Stratified Proportionate Disproportionate Cluster

  6. Probability Sample A sample in which each target population element has a KNOWN, NONZERO chance of being included in the sample

  7. Simple Random Sampling • Every unit within a population has a KNOWN and EQUAL probability of being chosen as the study sample

  8. Stratified Random Sampling • The chosen sample is forced to contain units from each of the segments, or strata, of the population • Proportionate: sample consists of units selected from each population stratum in proportion to the total # of units in the stratum • Disproportionate: sample consists of units selected from each population stratum according to how varied the units within the stratum are

  9. Cluster Sampling • Clusters of population units are selected at random and then all or some of the units in the chosen clusters are studied • Commonly institutions (e.g., schools, churches, prisons, etc.)

  10. Cluster Sampling Steps 1. The population is divided into mutually exclusive and exhaustive subsets (clusters) 2. A random sample of the subsets (clusters) is selected

  11. PROBABILITY SAMPLES

  12. Nonprobability Sample A sample that relies on personal judgment somewhere in the selection process and therefore prohibits estimating the probability that any population element will be included in the sample.

  13. Convenience Sample • A sample that is sometimes called an accidental sample because those included in the sample enter by accident in that they just happen to be where the study is being conducted when it is being conducted.

  14. Judgment Sample A sample that is sometimes called a purposive sample in that the sample elements are handpicked because they are expected to serve the research purpose. • Often selected because they have some information that the researcher wants

  15. Quota Sample A sample chosen in such a way that the proportion of sample elements possessing certain characteristics is approximately the same as the proportion of the elements with the characteristics in the population.

  16. NONPROBABILITY SAMPLES

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