Experimental designs

• Independent group design

  • 2 groups split by random allocation
  • Each group does different experimental condition
  • Measure DV for each group
  • Compare the results
• Independent group design AO3

  • the natural variation between individuals, ppt variables, may affect DV, making it look as IV caused it when it hasn't
  • less economical then repeated measures, ppt used ones
  • No order effect
  • PPt are less likely to guess the aim
• Repeated measures design:

  • Recruit a group of ppt
  • Complete condition 1 and the condition 2
  • Problem - ppt reactivity due to repeating measures
• Repeated measures AO3:

  • Doing both conditions - ppt bored, tired, allows to work out the aim, affects DV
  • Order effect - acts as a confounding variable, after 1st condition behave differently in 2nd
  • Demand characteristics are more likely as completed twice or more
  • More economical - need fewer ppt
• Counterbalancing - improves repeated measures:

  • all ppt split into 2 groups
  • one will do condition A first, condition B second
  • one will do condition B first, condition A second
• Matched pairs design:

  • recruit a group of ppt
  • find out what sorts of people we have in the group
  • recruit another group that matches the one for one
  • treat an experiment as independent groups
• Matched pairs AO3:

  • time-consuming
  • an exact match is rarely possible
  • if 1 ppt drops out, you lose 2 ppt's data
  • to solve some of the issues - members of each pair should be assigned to conditions randomly