Sampling

• What is a target population? [2]

  A group of people who are the focus of the researcher's interests, from which a smaller sample is drawn.
• What is a sample? [2]

  A group of people who take part in a research investigation. The sample is drawn from a target population.
• What are the 5 sampling techniques?

  • (R)andom Sampling
  • (O)pportunity Sampling
  • (S)ystematic Sampling
  • (V)olunteer Sampling
  • (St)ratified Sampling
• What is random sampling?

  Each member of the target population has equal chance of being selected
• How is random sampling conducted?

  1. A list of all members of the target population is obtained.
  2. All names are assigned a number.
  3. The sample is then generated through a lottery method.
• What is systematic sampling?

  When every nth member of the target population is selected
• What is stratified sampling?

  The variation of people in the sample is in direct proportion to the variation of people in the target population
• What is volunteer sampling?

  Ppts select themselves to participate in the study
• What is opportunity sampling?

  Selecting anyone who is willing and available
• How is systematic sampling conducted?

  1. A sampling frame is produced (e.g. list of target population ordered alphabetically)
  2. A sampling system is selected (nth number). May be determined randomly to reduce researcher bias
  3. Researcher works though sampling frame until completed
• How is stratified sampling conducted?

  1. Identify the different strata (e.g. subjects studied) that make up the target population
  2. The proportions needed for the sample to be representative are worked out (20% of students in college take maths so 20% of the sample should be maths students)
  3. The ppts that make up each stratum are selected using random sampling
• How is volunteer sampling conducted?

  • Place an advert in a newspaper that's likely to be seen by target population and wait for a response

  Or

  • Ask individuals if they would like to take part
• How is opportunity sampling conducted?

  Researcher asks people available at the time if they will complete the research
• What is a strength and a weakness of random sampling?

  • Avoids researcher bias - extraneous variables are equally divided between different groups
  • Time consuming - Names for target population can be difficult to obtain
• What is a strength and a weakness of systematic sampling?

  • Avoids researcher bias - once sampling system is selected researcher has no influence over who is chosen
  • Time consuming - names of the target population can be hard to obtain
• What is a strength and a weakness of stratified sampling?

  • Avoids researcher bias - once strata is created researcher has no influence over who is selected 
  • Not all individual differences are represented - strata cannot reflect all ways that people are different 
• What is a strength and a weakness of volunteer sampling?

  • More time efficient - participants come to you
  • Volunteer bias - those who volunteer often share the same characteristics (e.g. studious) so sample may still be bias in some way
• What is a strength and a weakness of opportunity sampling?

  • Time efficient - no need to make a list of members of target population or divide them into different strata
  • Unrepresentative of target population - sample is drawn from a very specific area