Experimental Designs

• What are the different types of exeperimental designs?

  independent groups, matched pairs and repeated measures
• Describe the independent groups design?


  The participants only perform in one condition of the independent variable (IV)
• Describe the repeated measures design?


  The same participants take part in all conditions of the IV
• Describe the matched pairs design?


  Pairs of participants are first matched on some variable that has been found to affect the dependent variable (DV), then 1 member of each pair does one condition and the other does another
• What are the strengths of independent groups design?


  There are no order effects, participants are less likely to guess the aims of the study so demand characteristics are eliminated
• What are the strengths of repeated measures design?


  • it controls for individual differences as same participants take part in both conditions allowing for a direct comparison with no individual factors impacting the outcome
  • less participants are needed so it is not as time consuming finding participants
• What are the strengths of a matched pairs design?

  • Demand characteristics and investigator effects aren’t a problem as participants only take part in 1 condition
  • No order effects
• What are the limitations for independent groups?


  No control of participant variables where different abilities of participants in the various conditions can cause changes to the DV

  Less economical that repeated measures as each person produces a single result only, which increase time and money spent
• What are the limitations of repeated measures design?


  • There are order effects for example, as each participants has to do at least 2 tasks this could create boredom so the participant may not do as well on the second task
  • It is also more likely that participants will workout the aim of the study when they experience all conditions
• What are the limitations of a matched pairs design?


  • It is time consuming and expensive to match as a

  large pool of potential participants is needed which can be hard to get so therefore less economical

  • It is difficult to know which variables are appropriate for the participants to be matched
• What can be a solution to the limitations of independent groups?


  Random allocation
• What is the solution to limitations of repeated measures?


  Counterbalancing
• What is meant by random allocation?


  Distributing participant characteristics across conditions of an experiment using random techniques
• How does random allocation solve independent measures?


  Solves individual differences as it ensures each participant has the same chance of being in one condition of the IV as another
• What is meant by counterbalancing?


  Participants should not complete each condition in the same order, so half of the participants should do the conditions in one order and the other half in an opposite order (ABBA technique)
• Explain the ABBA technique?


  P1 = AB

  P2= BA

  P3= AB

  P4=BA