Sampling

• Types of sampling


  Random

  Systematic

  Stratified

  Opportunity

  Volunteer
• What is random sampling?

  • All members of of the target pop. have an equal chance of being selected
  • HOW- complete list of all members of target pop, assign all names with a number, sample generated through 'lottery method' (can use a computer-based randomiser or picking numbers out of a hat)
• What is systematic sampling?

  • Where every nth member of the target pop is selected
  • HOW- produce a sampling frame containing a list of people in target pop. organised in a certain way (e.g. alphabetical order), nominate sampling system through self or randomised choice (e.g. every 6th person), work through frame till sample is complete
• What is stratified sampling?

  • Where the composition of the sample reflect proportions of people in certain sub-groups within the target pop. or wider pop.
  • HOW- researcher identifies the different strata that make up the pop., work out proportions needed to be representative, ppts that make up each stratum are selected using random sampling
• What is opportunity sampling?

  • Selecting anyone who is willing and available to participate
• What is volunteer sampling?

  • Involves ppts selecting themselves to be part of the sample
  • HOW- researcher can place advert or notice to attract willing ppts
• Random sample strengths


  • Free from researcher bias, researcher has no influence over who is selected preventing them from choosing ppts who they think will support their hypothesis
• Random sample limitations


  • Difficult and time-consuming, list of target pop may be difficult to obtain and may end up with a sample that is unrepresentative of pop.
  • Selected ppts may refuse to take part and therefore means researcher may have to rely on a different form of sampling
• Systematic sample strengths and limitations

  • :) Avoids researcher bias, selection method means researcher has no influence over ppts chosen, sample is likely to have higher validity
  • :) Fairly representative of target pop.
  • :( ppts may refuse
• Systematic sample strengths and limitations

  • :) Avoids researcher bias, selection method means researcher has no influence over ppts chosen, sample is likely to have higher validity
  • :) Fairly representative of target pop.
  • :( ppts may refuse
• Stratified sampling strengths and limitations

  • :) Avoids researcher bias, ppts are beyond influence of researcher due to strata divisions
  • :) Representative sample, designed to accurately reflect the composition of population, generalisations may be possible
  • :( Identified strata cannot reflect all differences, complete representation is therefore not possible, may decrease overall validity of generalisations
• Strengths and limitations of opportunity sample

  • :) Convenient in terms of time, effort and money, less effort to organise
  • :( Highly bias, unrepresentative of target pop. due to ppts being from a specific area so findings cannot be generalised (low ev)
  • :( Researcher bias, complete control over ppt selection and may avoid certain people they do not want in study
• Strengths and limitations of volunteer sample

  • :) Minimal input, less-time consuming and therefore beneficial to study
  • :( Volunteer bias, asking for volunteers may attract a certain profile or personality type which may affect overall findings and conclusions found, decreasing generalisability