Experimental design

• What are the types of experimental design?

  • Repeated measures
  • Independent measures
  • Matched pairs
• What is a repeated measures design?

  All participants receive all levels of the IV
• What are the strengths of repeated measures?

  • Each participant is compared to themselves, so no effect of individual differences
  • We need fewer participants as everyone experiences all levels of the IV
• What are the weaknesses of repeated measures?

  • Somethings can’t be investigated with this ie gender differences
  • Order effects - order of conditions may effect performance
• What is a solution to order effects?

  Counterbalancing - divide Ps into two groups

  A does task 1 first, then B does task 2 first

  This means order effects are cancelled out
• What is independent measures design?

  Ps are split into two groups, each one experiencing only one level of the IV
• What are the strengths of independent measures design?

  • No order effects
  • Less demand characteristics
  • Can study topics where the IV cannot be altered from person to person
• What are the weaknesses of independent measures?

  Researcher cannot control individual differences
• What is a solution for individual differences?

  Random allocation - randomly distribute the participant variables so not all Ps in one group will be similar
• How is random allocation done?

  Picking names out of a hat, random number generator
• What is a matched pairs design?

  We have two groups matched on characteristics that affect the DV (eg IV)
• What is a strength of matched pairs design?

  • Separate groups, so no order effects and no demand characteristics
  • Less affect of participant variables on the DV
• What are the weaknesses of matched pairs design?

  • Time consuming to match Ps up
  • Can’t control all participant variables
• What do we do to see which variables to match Ps on?

  Conduct a pilot study