Sampling Techniques

• What is Random Sampling?

  Random Sampling is a method of selecting a subset of individuals from a larger population in a way that each individual has an equal chance of being chosen
• What is Stratified Sampling?

  Participants are selected from different subgroups (strata) in the target population, in proportion to their frequency in their population
• What is a Volunteer Sample?


  A sample produced by asking people who are willing to participate
• What is an Opportunity Sample?


  A sample of participants selected purely because they were the most available
• What are the positives of Random Sampling?

  • It is unbiased as all members of the population have an equal chance of being selected
  • It is possible to choose a subgroup within a target population to make random selection easier
• What are the negatives of Random Sampling?

  • They require a lot of time to set up, due to needing a list of all possible participants in the target population before performing the random selection
  • After performing random selection, it is still biased as some participants may not agree in participating in the study, ruling out its randomness
• What are the positives of Stratified Sampling?

  • It's the most representative sampling technique
  • Specific subgroups can be chosen based on variables important to the researcher; this gives control over extraneous variables
• What are the negatives of Stratified Sampling?

  • The decision of what subgroups to include may cause bias and thus reduce the representativeness of the technique
  • It's a very lengthy process and participants may not agree to participate in the first place
• What are the positives of a Volunteer Sample?

  • Makes it easier to find budding participants willing to take part in longer studies
  • Allows for "purposive sampling", meaning you can study more specialised participants, eg. medical students
• What are the negatives of a Volunteer Sample?

  • There is a problem with participants being too helpful and playing into the desired characteristics made in the hypothesis/finding out the study's true aims
• What are the positives of Opportunity Sampling?

  • Most efficient method
  • Could be the only viable sampling technique for a study
• What are the negatives of Opportunity Sampling?

  • It will be inevitably biased, as certain aspects within researchers will make them choose certain participants; therefore ruins the representativeness of the study
• How do you perform Random Sampling?

  • Assign every possible participant in the target population a number
  • Use a random number generator to list out numbers
  • Use those the participants assigned with the numbers listed out by the number generator in the study
• How does Stratified Sampling work?

  If 10% of the target population is 10-12 years old, then 10% of the participating group must be 10-12 years old to retain represantiveness
• How do your perform a Volunteer Sample?

  • Advertise in a newspaper
  • Advertise in an area where you expect the right specialised participants for your study
• How do you perform an Opportunity Sample?

  • Select random people passing by wherever is convenient, eg. the school common room, shopping centre, park etc