Sampling

• What is the target population?

  The group of people who the researcher is interested in and from which a smaller sample is drawn
• What is the sample?

  A smaller group of people taken from the target population who take part in the research investigation
• Define sampling techniques

  The method used to select people from the population
• Define bias in terms of sampling

  Over or under representing a group within the sample selected
• Define generalisation

  Ability to apply findings from an investigation to the population
• Name the 5 types of sampling

  Random, systematic, stratified, opportunity, volunteer
• What is random sampling?

  Produced by using a random technique such that every member of the target population has an equal chance of being selected
• What is systematic sampling?

  Sample obtained by selecting every nth person (where n is any number)
• What is stratified sampling?

  Sample obtained by identifying subgroups (strata) in the target population and ensuring the sample reflects the proportions of people in each strata (randomly selected)
• What is opportunity sampling?

  Recruit people who are most convenient or available
• What is volunteer sampling?

  Participants select themselves to be part of the sample either through responding to advertisements in a newspaper or internet
• State one advantage of random sampling

  Unbiased - all members of the target population have an equal chance of selection
• State two disadvantages of random sampling

  1. Time consuming - requires a list of all members of population and then contact all those selected

  2. May not be truly representative of population e.g. might all come from same school/town
• State two advantages of systematic sampling

  1. Avoids researcher bias

  2. Should be representative
• State a disadvantage of systematic sampling

  Not truly unbiased/ random unless you selected a number using a random method
• State two advantages of stratified sampling

  1. Avoids researcher bias

  2. Representative sample - there is a proportional and randomly selected representation of subgroups
• State a disadvantage of stratified sampling

  Time consuming to identify subgroups
• State two advantages of opportunity sampling


  1. Convenient

  2. Cost-effective
• State two disadvantages of opportunity sampling

  1. Unrepresentative sample - drawn from a specific area e.g. if selected sample from people walking around town centre on Monday morning then would be unlikely to include profesional people

  2. Researcher bias
• State an advantage and disadvantage of volunteer sampling


  - Advantage: less time consuming

  - Disadvantage: volunteer bias - unrepresentative sample as may attract a certain 'type' of person