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SAMPLING

SAMPLING. Basic Concepts. Population: is the entire aggregation of cases that meet a designated set of criteria Sample: a subset of the units that compose the population Sampling: the process of selecting portion of the population

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SAMPLING

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  1. SAMPLING

  2. Basic Concepts • Population: is the entire aggregation of cases that meet a designated set of criteria • Sample: a subset of the units that compose the population • Sampling: the process of selecting portion of the population • Representativeness: the key chch of the sample is close to the population

  3. Example • Studying the self esteem and academic achievement among nursing college students • Population: all student who are enrolled in any college level of nursing • Sample: nurse college student at the University of Jordan

  4. Strata: two or more subgroup • Sampling bias: excluding any subject without any scientific rational. Or not based on the major inclusion and exclusion criteria.

  5. Non-probability A. Convenient sampling or accidental sampling. • To use the more convenient available people or objects • Snowballing or networking sampling • It is the weakest form of sampling

  6. Non-Probability B. Quota sampling • The researcher defines the population and then set a proportion form which he will choose form each segment of the population

  7. Non-Probability C. purposeful and theoretical sampling • The researcher’s knowledge about the population used to select the sample • Theoretical sampling used as of the progression of the study. More subject can be added as a preliminary analysis may induce.

  8. Probability Sampling • Simple random sampling. E.g., tables • Stratified random sampling. Gender, age • Cluster sampling. City, neighborhood, block, house • Systematic sampling. Selecting every kth case.

  9. Sample Size • The larger the sample size the better the Representativeness • The techniques of power analysis • Computer program such as PASS, NCSS

  10. Considerations • Homogeneity vs. heterogeneity • Effect size: r/s between I & D variables • Attrition: N of subjects decline the study

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