types of experimental design

• repeated measures: the same ppts take part in each condition of the IV 


  • fewer people are needed as they take part in all conditions, saving time.
  • ppts variables are reduced, as the same ppts are used in each condition.
  • order effects
  • possible demand characteristics from repeating the experiment.
  • to resolve, use counterbalancing - e.g. group 1 does AB and group 2 does BA, order effects will still occur, however since they occur equally in both groups they balance each other out in the results.
• independent groups: different ppts are used in each condition of the IV


  • avoids order effects
  • more people are needed than with repeated measures.
  • ppt variables in the group may affect results.
  • to resolve this, the ppts should be randomly assigned to their independent groups, this should ensure the groups are similar on average, (reducing ppt variables.)
• matched pairs: each condition uses different but similar ppts, with an effort made to match the ppts in terms of any important characteristic. 


  • reduces ppt variables
  • avoids order effects
  • time-consuming - trying to find closely matched pairs - impossible to match people exactly, unless they are identical twins.
  • if one ppt drops out, you lose two ppt's data.
  • to resolve this, members of each pair should be randomly assigned to conditions, (this does not resolve all issues.)