Sampling

• Population: A group of people who are the focus of the researcher’s interest, from which a smaller sample is drawn.
• Sample: A group of people who take part in a research investigation. The sample is drawn from a population and is presumed to be representative of that population.
• Sampling techniques: The method used to select a sample of the population.
• Bias: In the context of sampling, when certain groups are over/under represented within the sample selected. For instance there may be too many young people, this limits the extent to which generalisations can be made to the target population.
• Generalisation: The extent to which findings and conclusions from a particular investigation can be broadly applied to the population. This is possible if the sample of participants is representative of the target population.
• Random sample:

  • All members of the target population have an equal chance of being selected.
  • The first step is to have a list of everyone in the target population.
  • Then names may be randomly selected through a lottery method to choose the sample.
• Systematic sample:

  • When every Nth member of the target population is selected, for example every third house on a street.
  • A sampling frame is produced and then every Nth person is nominated.
  • May begin from a randomly determined start to reduce bias.
• Stratified sample:

  • The sample reflects the proportions of people in a certain subgroup.
  • Different strata’s are identified and then it is worked out how many people are needed for each strata.
  • Each person is randomly selected for each group.
• Opportunity sample:

  • This is when the researcher decided to select anyone who happens to be willing and available.
• Volunteer sample:

  • Participants select themselves to be in the sample.
  • Could be responding to an advert or noticboard.
• Random Sampling Evaluation:

  • Strengths- Unbiased, internally valid.
  • Limitations- Time-consuming, difficult, need a sample frame, unrepresentative
• Systematic sample Evaluation:

  • Strengths- Objective, unbiased
  • Limitations- time consuming, volunteers may refuse
• Stratified sample Evaluation:

  • Strengths- Representative, easy to generalise
  • Limitations- stratification isn’t perfect
• Opportunity sample Evaluation:

  • Strengths- convenient, less costly
  • Limitations- bias
• Volunteer sample Evaluation:

  • Strengths- easy, less time consuming
  • Limitations- volunteer bias