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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




stratified random sampling1
Stratified Random Sampling

Disproportionate to their representation in the population




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