sampling

• what is sampling?

  • selecting participants from a target population which is too big to study in its entirety so sampling techniques are used to choose a representative sample
• what are the 5 sampling techniques?

  • random
  • systematic
  • opportunity
  • volunteer
• random sampling

  • every member of the target population has equal chance of being selected
  • identifying everyone in the target population and then selecting the number of participants needed to give everyone an equal chance of being selected
  • picking names out a hat, random name generator
• evaluating random sampling

  +free from researcher bias

  -difficult and time consuming to ensure everyone has an equal chance of being picked

  -some people who are picked may be unwilling to take part
• systematic sampling

  • a predetermined system is used to select participants
  • e.g. every fifth person is chosen
• evaluation of systematic sampling

  +free from researcher bias

  -may not be truly unbiased as every Nth person may have a common characteristic e.g. being right handed. therefore it may not be representative of the whole target population
• stratified sampling

  • identifying subgroups within a population
  • participants are obtained from each stratum (layer/category) in proportion to their occurrence within the population
• evaluating stratified sampling

  +largely free from researcher bias as sample is randomly generate once the subcategories have been identified

  -difficult and time consuming to accuratley identify the sub groups
• opportunity sampling

  • selecting anyone who is willing to take part
• evaluating opportunity sampling

  +convenient - quicker, cheaper and easier to obtain participants

  -bias - if a sample is drawn from various universities, only students will be taking part

  -increased risk of investigator effects as researcher has complete control over who they approach
• volunteer sampling

  • people who self select to take part either by volunteering or responding to an advert
• evaluating volunteer sampling

  +quicker and easier to obtain compared to other methods

  -sample is likely to be bias

  -a particular type of person is likely to take part and only those who see the advert