sampling

• Population

  • The large group of people that a researcher is interested in studying
  • Eg = college students from the North West
• Sample

  • It is usually not possible to include all members of the population in the study, so a smaller group is selected (the sample)
• generalisation

  • The sample that is drawn should be representative of the population so generalisations can be made
• bias

  • Most samples are biased in that certain groups (eg men, students, professionals etc) may be over- or under-represented
• random sample

  • Equal chance = every person in the target population has an equal chance of being selected
  • How = lottery method = all members of the target population are given a number and placed in a hat or computer randomiser
  • Strength = potentially unbiased
  • means CVs/EVs are controlled, enhances internal validity
  • Limitation = time consuming and may not work
  • Complete list of population is hard to get AND some pps mat refuse to take part
• systematic sample

  • Using a set system = pps are selected using a set ‘pattern’ (sampling frame) (eg list in alphabetical order)
  • How = every nth person is selected from a list of the target population
  • Strength = unbiased
  • First item is usually selected at random => objective method
  • Limitation = time and effort
  • Compete list of population is require - may as well used random sampling
• stratified sample

  • strata = sample reflects proportions of people in certain subgroups (strata) within a population
  • How = subgroups (or 'strata') are identified (eg gender or age groups) - the relative percentages of the subgroups in the population are reflected in the sample
  • Strength = representative method
  • Characteristics of the target population are represented => generalisability more likely than other methods
  • limitation = stratification is not perfect
  • Strata cannot reflect all the ways in which people are different => complete representation is not perfect
• opportunity sample

  • People who are simply most available (ie the ones who are nearest/easiest to obtain)
  • How = ask people nearby (eg ask the students in your class to take part or ask people who walk past you at a shopping centre)
  • Strength = quick method
  • Convenient becuase you just make use of people who are closest => makes it cheaper and one of the most popular sampling methods
  • Limitation = inevitably biased
  • Sample is unrepresentative of target population as it is drawn from a very specific area (eg one street in town) => means findings cannot be generalised
• volunteer sample

  • self-selecting = In a volunteer sample, participants select themselves
  • How = advertise (eg place an advert in a newspaper or ask people to put hands up to volunteer)
  • Strength = participants are willing
  • pps have selected themselves and know how much time and effort is required (=> likely to engage more than people stopped in the street)
  • Limitation = volunteer bias
  • pps may share certain traits (eg want to be helpful) AND thus may response to cues and generalisation limited