sampling methods

• Target population and samples

  • Group of people researcher is studying
  • sample of participants from target population
• Generlisability and representativeness

  • A sample should reflect the characteristics seen in the target population as far as possible.
  • The closer it is, the more representative it is.
  • If our sample is representative, we can then generalise our results to the whole target population.
• Bias:

  • hard to obtain a completely representative sample that reflects target population
  • Our sample is often biased to some degree.
• Random sampling:

  • This involves identifying everyone in the target population
  • and then selecting the number of participants you need in a way that gives everyone in the population an equal chance of being picked e.g. taking names out of a hat
• strengths of random sampling:

  • No researcher bias- equal chance of being selected
  • Gives a representative sample
• Weakness of random sampling:

  • Takes time and effort as a list of everyone in the target population needs to be obtained and randmly selected. Effort may not be worth it
• Opportunity sampling:

  • It consists of taking the sample from people who are available at the time the study is carried out and fit the criteria you are looking for.
• Strength of opportunity sampling:

  • Easiest, quickest and cheapest to get sample- choosing people nearby
• Weakness of opportunity sampling:

  • Likely to be unrepresentative of the population if its drawn from one place
  • Difficult to generalise- reduces generalisability of results
• Systematic sampling

  • when a consistent system/strategy is used to collect your sample
  • selecting every nth person from a list of people in the target population
• Strengths of systematic sampling:

  • Avoids researcher bias as the researcher has no say who is selected
  • more representative
• Weakness of systematic sampling:

  • Although it is usually representative it can be biased
  • sample may consist of one particular group of people
  • this decreases representativeness
• Stratified sampling:

  • involves classifying the population into categories and then randomly choosing a sample which consists of participants from each category in the same proportions as they are in the population
• Strengths of stratified sampling

  • Most representative sampling method as sub-groups are reflected in proportion of the numbers in the target population
• Weakness of stratified sampling

  • Very time-consuming and difficult to do- takes a while to identify proportions of subgroups and then recruit participants
  • discourages researchers from using this method