experimental design

• What are the types of experimental design?


  • Independent groups
  • Repeated measures
  • Matched pairs
• Outline independent grouping


  different participants are randomly allocated to take part in each experimental condition
• What are the strengths of independent grouping?


  • order effects (responses affected by order of conditions) are not observed
  • data collection is less time-consuming
  • less chance of demand characteristics
• What are the weaknesses of independent grouping?


  • different participants for each condition = difficult+expensive
  • group differences may be due to participant variables
• Outline repeated measures


  participants are the same and allocated to all groups in a experiment
• What are the strengths of repeated measures?


  • not affected by participant variables
  • hiring of participants = cheaper+easier
• What are the weaknesses of repeated measures?


  • risk of demand characteristics
  • data is lost if participant drops out
  • order effects
• Outline matched pairs


  participants take part in one experimental condition but are specifically similar in relevant characteristics (e.g, IQ, age, gender, etc)
• What are the strengths of matched pairs?


  • order effects not observed
  • reduced risk of participant variables
  • less risk of demand characteristics
• What are the weaknesses of matched pairs?


  • different participant for each condition = difficult+expensive
  • matching is a complex / subjective process
• What is the definition of a single-blind procedure?

  only the researcher knows the treatment/intervention the participant is receiving

  e.g, taste-testing
• How might a single-blind procedure reduce demand characteristics?

  participant cannot change behaviour or is unaware of the true aim of the research
• What is the definition of a double-blind procedure?

  neither the researcher nor patient know treatment/intervention

  e.g, use of placebo in drug testing