Experimental Designs

• Experimental Design


  Refers to the way in which we put our PPs into groups in the experiments
• What is Independent Groups?

  1. PPs are randomly allocated to one condition of the IV
  2. One group undergoes one condition and other group undergoes the other condition
• Strengths of Independent Groups

  • No order effects as the people only take part in one condition
  • Same materials can be used for the other condition so time and money can be saved
  • PPs cannot work out the aim of the study as they only take part in one condition reducing demand characteristics
• Weaknesses of Independent Groups

  • Participant variables (individual differences) such as age and gender may affect the results
  • More PPs are needed as different people take part in different conditions
• What is Repeated Measures?

  PPs take part in both conditions of the IV
• Strengths of Repeated Measures

  1. Half the number of people needed as they take part in both conditions
  2. The PPs are the same so there is no individual differences
• Weaknesses of Repeated Measures

  • Order effects may happen such as boredom and fatigue as PPs have taken part in both conditions
  • PPs may guess the aim of the study so demand characteristics may occur affecting the results
• How can you limit order effects in a repeated measures design?

  By counterbalancing
• What is counterbalancing?


  An attempt to control order effects in a repeated measures design: half the participants experience the conditions in one order and the other half in the opposite order
• How is counterbalancing done?

  • In one group half the PPs take part in Condition 1 and then Condition 2
  • The other half then take part in Condition 2 and then Condition 1
  • Counterbalancing attempts to balance out the order effects
• What is Matched Pairs?

  1. PPs are matched based on similarities or key characteristics e.g gender or IQ
  2. One of the pair is then randomly allocated to Condition A and the other to Condition B and undertake different conditions of the IV
• Strengths of Matched Pairs

  • Reduces the number of characteristics thought to influence the DV making matching easier and saves time
  • Conduct a pilot study to identify the key characteristics relevant to the study
• Weaknesses of Matched Pairs

  • Time consuming to test PPs and match them based on important characteristics
  • Difficult to reduce all participants variables that may affect the DV