Sampling methods

• Target population

  The large group of people the researcher wishes to study
• Random sample


  • Every member of the target population has an equal chance of being selected
  • Researcher must identify all members of the target population, number each person, and then draw out the required number of people
• Opportunity sampling


  • Choosing people who are members of the target population and are available and suitable to take part
  • Quick, easy way to collect people for a study
• Systematic sampling


  • Selecting every nth member of the target population
  • Unbiased because the researcher cannot choose the individuals
  • Not random because the people who are first to sixth in the population do not get a chance to be selected
• Stratified sample


  • Different subgroups in the target population are identified
  • People are selected randomly from these subgroups in proportion to their numbers in the target population
• Strengths and Weaknesses

  Random

  No researcher bias

  Likely to be representative

  Time-consuming

  Opportunity

  Quick and easy

  Not likely to be representative and may have researcher bias

  Systematic

  Simple procedure with no researcher bias

  Sample may not be representative

  Stratified

  Very representative

  Very time-consuming