experimental designs

• Independent groups

  • One group does condition A and a second group does condition B
  • participants should be randomly allocated to experimental groups
• independent groups evaluation:

  • Strength = no order effects:
  • pps only tested once so cant practice or become bored/tired
  • This controls an important CV
  • Strength = wont guess aim:
  • pps only tested once so unlikely to guess research aims
  • => behaviour may be more natural
  • Limitation = participant variables:
  • pps in the 2 groups are different, acting as EV/CV
  • May reduce validity of the study
  • Limitation = less economical:
  • Need twice as many pps as repeated measures for same data
  • More time spent recruiting => more expensive
• repeated measures

  • Same participants take part in all conditions of an experiment
  • The order of conditions should be counterbalanced to avoid order effects
• repeated measures evaluation

  • Strength = participant variables:
  • Person in both conditions has same characteristics
  • Controls an important CV (reduces individual differences)
  • strength = fewer participants:
  • Half number of participants is needed than in independent groups
  • Less time spent recruiting pps
  • Limitation = order effects are a problems:
  • pps may do better or worse when doing a similar task twice AND practice/fatigue effects
  • Reduces validity of results
  • Limitations = pps guess aims
  • pps may change their behaviour
  • Reduces validity of results
• matched pairs

  • 2 groups of participants are used but they are also related to each other by being paired on participant variable(s) that matter for the experiment
• matched pairs evaluation

  • Strength = participant variables
  • pps matched on a variable that is relevant to the experiment
  • This controls pp variables and enhances the validity of the results
  • Strength = no order effects
  • pps are only tested once so no practice or fatigue effects
  • Enhances the validity of results
  • Limitation = matching is not perfect
  • Matching is time-consuming and can’t control all relevant variables
  • Cannot address all pp variables
  • Limitation = more participants
  • Need twice as many pps as repeated measures For same data
  • More time spent recruiting which is expensive