Sampling

• What are the different sampling methods?

  • Random sampling
  • Systematic sampling
  • Stratified sampling
  • Opportunity sampling
  • Volunteer sampling
• What is random sampling?

  Every member of the target group has an equal chance of being selected for the sample
• What is a strength of random sampling?

  Achieves a representative sample
• What are the weaknesses of random sampling?

  • Small minority groups may skew results
  • Can be impractical, if the target group is too large
• What is systematic sampling?


  Using a predetermined system to select the participants from a target group ie every fourth person in a list
• What are the strengths of systematic sampling?

  If the list is randomised, it is unbiased and gets a representative sample
• What are the weaknesses of systematic sampling?

  If the list isn’t randomised, it doesn’t give an equal chance of selection to the whole group

  eg if it is in alphabetical order, the first person on the list would have no chance of being chosen
• What is stratified sampling?

  The target group is divided into sections, each showing a key characteristic which should be present in the sample

  eg we want a sample of people with SZ and in the target population 60% are male, we have 60% males in our sample
• What is a strength of stratified sampling?

  Avoids misrepresentation
• What are the weaknesses of stratified sampling?

  • Time consuming
  • Each key characteristic must be selected carefully
• What is opportunity sampling?

  Participants are selected based on their availability and accessibility at the time of the study
• What are the strengths of opportunity sampling?

  Easy and inexpensive
• What are the weaknesses of opportunity sampling?

  Subject to bias, a sample at 10am wouldn’t include office workers, teachers etc so would be unrepresentative
• What is volunteer sampling?


  Participants are selected based on their willingness to participate
• What is a strength of volunteer sampling?

  Achieves a large sample size as reaches a large audience
• What are the weaknesses of volunteer sampling?

  Those who volunteer may all have similar characteristics or be interested in the topic, leading to an unrepresentative sample