selection of participants

• convenience sampling


  participants who are easily accessable

  • time and effort is low but bias can be high
• snowballing sampling


  initial participants invite other people

  • time and effort is low but unlikely to represent whole population
• random sampling


  names are randomly selected

  • bias is minimum but time and effort is high
• stratified sampling


  population broken into subgroups based on characteristics, then selected

  • represnetative but time and effort is high
• random allocation


  random distribution of participants into experimental and control groups

  • reduce researcher bias and increase generalisability of results