Sampling

• What does population mean?

  The large group of people that a researcher is interested in studying.
• What is a sample?

  As it‘s not possible to include all members of the target population in the study, the researcher selects a smaller group which is the sample.
• What is generalisation?

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

  Most samples are biased as in certain groups it may be over or under represented.
• What is random sampling?

  A sophisticated form of sampling in which all members of the target population have an equal chance of being selected.
• Advantage of random sampling

  Random sampling is potentially unbiased meaning that CVs and EVs are controlled which enhances internal validity.
• Disadvantage of random sampling

  Random sampling is difficult and time-consuming as a complete list of the target population is hard to get.
• What is systematic sampling?

  • When nth member of the target population is selected.
  • A sampling frame is produced, which is a list of people in the target population organised into.
• Advantage of systematic sampling

  It is unbiased as the first item is usually selected at random.
• Disadvantage of systematic sampling

  This method is time-consuming as a complete list of the population is required, meaning researchers may use random sampling and this method is useless.
• What is stratified sampling?

  • Sample reflects proportions of people in certain strata within a population.
  • Strata are identified and the relative percentage of the subgroups in the population are reflected in the sample.
• Advantage of stratified sampling

  Produces a representative sample as its designed to accurately reflect the composition of the population, meaning that generalisation of findings becomes possible.
• Disadvantage of stratified sampling

  Stratification is not perfect as strata can’t reflect all the ways in which people are different, meaning a complete representation isn’t possible.
• What is opportunity sampling?


  • Researchers select anyone who happens to be willing and available.
  • The researcher asks whoever is around at the time of their study.
• Advantage of opportunity sampling

  It’s a quick method as it is convenient as you just make use of the people who are closest, which makes it cheaper and one of the most popular sampling methods.
• Disadvantage of opportunity sampling

  Can be biased as the sample is unrepresentative of the target population as it’s drawn from a very specific area, so findings can’t be generalised to the target population, and the researcher has complete control over the selection of participants, so may avoid people they don’t like the look of, which is researcher bias.
• What is volunteer sampling?

  • Participants select themselves to be part of the sample.
  • Researcher may place an advert in a newspaper.
• Advantage of volunteer sampling

  Participants are willing as they have selected themselves so they are likely to be more engaging.
• Disadvantage of volunteer sampling

  Volunteer bias is a problem as participants may share certain traits therefore they respond to cues and generalisation limited.