sampling

• Sample


  A subset of individuals selected from the target population to represent it in a study.
• Sampling


  when researchers puck a sample from a population
• Volunteer sampling


  when a researcher posts an advert and people volunteer to be a participant in the study
• Pros of volunteer sampling


  • It is easy
  • can reach many people
• Cons of volunteer sampling

  • Not very representative of whole population
• Opportunity sampling


  • when a researcher approaches members of the population who are willing and available to be participants
• Pros of opportunity sampling

  • quick and easy way to get participants
• Cons of opportunity sampling

  • sample will not be very representative of the population
• Systematic sampling


  when researchers select every nth person from the entire population
• Pros of systematic sampling

  • More representative of population than others
• Cons of systematic sampling

  • difficult to get list of entire population
  • not always representative if there is a pattern
• Random sampling


  picking randomly from a list of the entire population so that everyone has an equal chance of being a participant.
• Pros of random sampling

  • most likely to be representative of the whole population
• Cons of random sampling

  • can be difficult to randomise
  • time consuming
  • representative sample is not guaranteed
  • need a list and a way to pick randomly
• Stratified sampling


  when researchers sample so that their sample has the same proportion of each subgroup as the total population
• Pros of stratified sampling

  • Best way to make sure sample represents whole population
  • results likely to generalise to the whole population
  • high population validity
• Cons of stratified sampling

  • researchers may miss out an important subgroup by mistake
  • sample may not be completely representative
  • time consuming
  • difficult
• How researchers come up with a stratified sample

  • Identify subgroups in a population
  • Identify how many from each subgroup are needed to have the same proportion as the original population
  • randomly sample from each subgroup to get that number