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Sampling. Census and Sample (defined). A census is based on every member of the population of interest in a research project A sample is a subset of the population. Characteristics of a Sample. Representative of the larger population Can be more efficient in terms of cost, time

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census and sample defined
Census and Sample (defined)
  • A census is based on every member of the population of interest in a research project
  • A sample is a subset of the population
characteristics of a sample
Characteristics of a Sample
  • Representative of the larger population
  • Can be more efficient in terms of cost, time
  • Generalizable results
  • Can reflect animate or inanimate populations
the sampling frame
The Sampling Frame
  • The list of elements from which a sample may be drawn
  • Defines the criteria on which elements will be selected
  • But, does not ensure that some elements will not be excluded or accurately represented
    • Sample frame error
sampling unit
Sampling Unit
  • A single element or group of elements subject to selection in a sample
    • Ex. An 18 to 24 year old male with senior academic classification
    • Ex. Grocery retailers that gross $30,000 in revenues monthly
sampling methods
Sampling Methods

Probability sampling

  • Elements each have a known, calculable non-zero probability of inclusion
  • The probability of inclusion is predictable across elements
sampling methods1
Sampling Methods

Non-probability sample

  • Sampling does not ensure a representative range of elements found in the larger population
forms of probability sampling
Forms of Probability Sampling
  • Simple random sampling
    • Each member of the population has a known, equal chance of being selected
    • Allows comparable estimates without surveying the entire population
forms of probability sampling1
Forms of Probability Sampling
  • Systematic random sampling
    • Sampling occurs based on a skip interval system where every nth member is selected from the population
    • Each element at the skip level is selected and interviewed
systematic random sampling
Systematic Random Sampling
  • Directory of Physicians in the Gainesville, FL area
forms of probability sampling2
Forms of Probability Sampling
  • Stratified random sampling
    • Sampling based on applying weights to population stratas
      • Proportionate vs. disproportionate stratums
    • Appropriate when the population is non-homogenous or has wide variations
stratified random sampling
Stratified Random Sampling

Proportionate to their representation in the population

65%

23%

12%

stratified random sampling1
Stratified Random Sampling

Disproportionate to their representation in the population

33%

34%

33%

cluster sampling
Cluster Sampling
  • Segmenting the population to sample based on geography
    • Postal codes, electoral constituencies, states, regions
multi stage sampling
Multi-stage Sampling
  • Two-step process
  • Select a primary sample based on a pre-specified sampling method
    • 35 – 45 YO Women
  • Then, selecting a secondary sub-sample from within the larger sample group
    • 35 – 45 YO Women who actively invest in the stock market
forms of non probability sampling
Forms of Non-probability Sampling
  • Convenience sampling
    • Participants are selected based on convenience and accessibility
    • Quick, uncomplicated, low in cost
    • Useful for exploratory research or quick info
forms of non probability sampling1
Forms of Non-probability Sampling
  • Judgment sampling
    • Participants are selected based on an expert’s judgment of the characteristics of a representative sample
    • Example: the “typical” customer
forms of non probability sampling2
Forms of Non-probability Sampling
  • Quota sampling
    • Attempts to ensure demographic characteristics of interest are represented in the sample proportionately to their representation in the population
    • Sample based on population percentiles
forms of non probability sampling3
Forms of Non-probability Sampling
  • Snowball sampling
    • Initial respondents are selected by probability sampling techniques
    • Additional respondents are obtained by referral from initial respondents