Experimental Design

• how you allocate your participants to the varying conditions of your experiment
• independent groups


  participant only takes part in 1 level of the IV

  -IV naturally occurring(gender/age), must use design

  -randomly allocated to one level of IV (equal chance)
• strengths of independent groups

  -only take part in one condition, less likely to guess aim of study, reducing effects of demand characteristics

  -no order effects that can reduce validity of findings
• weakness of independent groups

  -problem with participant variables affecting DV rather IV (personality)

  -more participants required for type of design compared to repeated measures
• repeated measures


  -participant takes part in all levels of the IV

  -cannot be used if IV is naturally occurring

  -must be counterbalancing (ABBA design)
• strengths of repeated measures

  -design eliminates any effect of participant variables, as all participants take part in all conditions (controlled)

  -fewer participants required than independent groups
• weakness of repeated measures

  -take part in all conditions, chance of demand characteristics affecting the study (work out aim behave in way to fulfill rather than true behavior)

  -other effects affect findings and reduce validity

  • practice effect: get better at task completed similar one
  • fatigue effect: more taskes do more tired become
  • boredom effect: repeating similar tasks bore participants
• matched pairs


  -participants are matched on a variable researches wish to control (gender, age, ethnicity)
• strengths of matched pairs

  -participant variables controlled and eliminated, as participants have been matched

  • psych can be more confident IV is affecting Dv rather than participant variables
• weakness of matched pairs

  -find participants who are matched on all variables (time consuming)

  -may be one or two participant variables that are overlooked with initial matched (could affect DV rather than IV)

  -cannot control every participant variable