Sampling

• target population


  large group of individuals the researcher is intrested in studing e.g. students in year 12
• sample

  smaller group within target population
• why do samples need to be representative

  to generalise findings (must match the characteristics of the target population e.g. ethnicity, gender, age)
• random sampling

  all members of target population have equal chance of getting selected
• +/- of random sampling

  + free from researcher bias

  - may be unrepresentative

  - difficult & time-consuming

  - selected Ps may refuse to take part
• systematic sampling

  every nth person in the target population is selected e.g. every 5th house on a street
• +/- of systematic sampling

  + avoids researcher bias

  + fairly representative

  - difficult & time-consuming

  - selected Ps may refuse to take part
• stratified sampling

  sample reflects the prportions of people in sub-groups within target population
• +/- of stratified sampling

  + avoids researcher bias

  + representative

  - starta can't reflect all ways Ps are different

  - difficult & time-consuming

  - selected Ps may refuse to take part
• opportunity sampling


  select anyone who happens to be willing and able at the time of their study e.g. market research
• +/- of opportunity sampling

  + convieniant

  - unrepresenative

  - researcher bias
• volunteer sampling


  Ps selected themselves to be part of the sample - self selection
• +/- of volunteer sampling

  + convenient

  - volunteer bias (keen-beans)