Experimental designs:

• What are the three types of experimental design?

  1. Repeated measures
  2. Independent groups
  3. Matched pairs
• What is repeated measures?

  The same group of participants are tested in all conditions of the experiment
• What are the strengths of a repeated measures experimental design?

  • The researcher is comparing the same ppts in each condition. This means that ppt variables do not act as an extraneous variable
  • Less ppts are required than an independent groups design to end up with the same amount of data
• What are the limitations of a repeated measures design?

  • Order effects act as an extraneous variable. Ppts may underperform in the second condition due to tiredness/boredom or over perform in the second condition due to practice
  • Demand characteristics are more likely to act as an extraneous variable. This is because the ppts are more likely to be able to guess the aim of the study if they are taking part in all conditions
• What is an independent groups design?

  A different group of participants are tested in each condition of the IV
• What are the strengths of an independent groups design?

  • Order effects do not act as an extraneous variable. Ppts only experience one condition
  • Demand characteristics are less likely to act as an extraneous variable. This is because ppts are less likely to be able to guess the aim of the study if they are only taking part in one condition
• What are the limitations of an independent groups design?

  • The researcher is comparing different ppts in each condition. This means that ppt variables act as an extraneous variable. Ppts in one condition may perform better because they have certain characteristics in common rather than because of the condition of the IV they experience.
  • More ppts are required than a repeated measures design to end up with the same amount of data
• What is a matched pairs design?

  Ppts are matched into pairs based on a variable that is relevant to the DV (e.g. age)

  One member of each pair is tested in each condition of the IV
• What are the strengths of doing a matched pairs design?

  • Ppt variables are less likely to act as an extraneous variable because ppts have been matched
• What are some limitations of doing a matched pairs design?

  • Matching ppts can be time consuming and expensive
  • Ppts are only matched on variables that are known to be relevant. there could be other unknown variables that ppts are not matched on. Any differences that are found between the two conditions could be due to these unknown ppt variables