Experimental Designs

• What are experimental designs?

  The different ways in which participants can be organised in relation to the experimental conditions.

  --> experimental designs: independent measures, repeated measures or matched pairs
• Experimental design: Independent measures

  Independent measures = participants are allocated to different groups where each group represents just one experimental condition.

  --> positives:

  • less demand characteristics
  • no order effects (effect caused by order in which conditions are done)

  --> negative:

  • participant's variables e.g. IQ, motivation, gender
• Experimental design: Repeated measures

  Repeated measures = all participants take part in all conditions of the experiment

  --> positive:

  • no participant variables (same data of participants in both conditions)

  --> negatives:

  • more demand characteristics
  • order effects (however can be resolved by counterbalancing)
• What is counterbalancing?

  An attempt to control for the effects of order in a repeated measures design: half the participants experience the conditions in one order, and the other half in the opposite order.
• Experimental design: Matched pairs

  Matched pairs = Pairs of participants are first matched on some variable(s) that may affect the dependent variable. Then one member of the pair is assigned to Condition A and the other to Condition B.

  --> positives:

  • not as many demand characteristics
  • no order effects
  • less participant variables

  --> negatives: (why it's the least used experimental design)

  • difficult to match accurately on all relevant participant variables
  • takes time