Sampling Techniques

• Sampling


  The process of selecting a representative group of participants from the population under study
• Target population


  The total group of people we are interested in studying
• Sample


  The group of people who take part in the investigation
• Representative sample


  A group that closely matches the characteristics of its population as a whole
• It's often impossible to study every single person in a target population so psychologists select a sample of the population that is likely to be representative of the target population we are interested in
• Sampling technique


  The method used to gather the sample from the target population
• Sampling techniques


  • Opportunity (aka convenience sampling)
  • Volunteer (aka self-selected sampling)
  • Systematic sampling
  • Random sampling
  • Stratified random sampling
  • Purposive sampling
  • Snowball sampling
• Opportunity/Convenience sampling


  • Gathering a sample by finding participants who happen to be available at a convenient time or who are easily at hand
  • May include use of a pre-existing group that are already assembled
• Volunteer/Self-selected sampling


  • Involves recruiting volunteers to participate in the study usually in response to an advertisement in the local community or over the Internet
  • Participants approach the researchers to volunteer for a study
• Systematic sampling


  • A sampling technique that uses a predetermined system to select the participants from a target group
  • For example, every fourth person in a list could be used in the sample
• Random sampling


  • A type of probability sampling where everyone in the entire target population has an equal chance of being selected
  • Random samples require a way of naming or numbering the target population and then using some type of raffle method to choose those to make up the sample
• Stratified random sampling


  • Attempts to make a sample that reflects the sub-groups within a target population
  • Divides the population into smaller groups, or strata, based on shared characteristics
  • A random sample is taken from each stratum in direct proportion to the size of the stratum compared to the population
• Purposive sampling


  • Participants are selected based on characteristics or specific experiences relevant to the topic
  • May involve the use of self-selected or snowball sampling to obtain a sample that matches the criteria of the study
• Snowball sampling


  • A group of initial participants (called ―seeds‖) invite others to participate in the study
  • The sample keeps growing in size until the desired size has been reached
  • It is particularly useful when studying ―hidden populations‖ (people who do not want others to know about them or who are hard to find)
• Sampling bias


  Errors that can occur in research studies by not properly selecting participants for the study which results in a sample that does not reflect the target population
• WEIRD is an acronym coined by Henrich, Heine & Norenzayan and refers to samples that are drawn from populations that are Western, Educated, Industrialised, Rich, and Democratic
• Key concepts


  • Sample
  • Target population
  • Sampling technique
  • Random sampling
  • Stratified random sampling
  • Opportunity/convenience sampling
  • Self-selected/volunteer sampling
  • Purposive sampling
  • Snowball sampling
  • Sampling bias