Experimental designs

• Experimental design


  How the researcher uses the participant sample in combination with the different levels of independent variable
• Experimental designs


  • Repeated measures design
  • Independent groups design
  • Matched pairs design
• Independent groups design


  • Groups are independent of each other, different sets of people in each condition
  • Data collected is called unrelated data
• Problem with independent groups design

  Change measured may not be due to the change in independent variable, but be due to participant variables
• Repeated measures design


  • Each participant completes both conditions
  • Data collected is called related data
• Problem with repeated measures design


  Order effects may occur, such as practice or boredom
• Counterbalancing


  Getting half the participants to do condition A then B and the other half B then A to balance the influence of order effects
• Counterbalancing


  Controls order effects but doesn't eliminate them
• Matched pairs design


  • Two separate groups of participants are used, one for each condition
  • Participants are matched on a characteristic that may influence the result
  • Results of each pair in each condition are compared as related data
• Advantages of matched pairs design

  Reduces the effect of participant variables and removes order effects
• Disadvantages of matched pairs design

  Takes longer to set up, needs more participants, and participants are similar but not identical
• The researcher has choices in how they set up the experiment, but of course there are positives and negatives to each design
• The researcher is comparing each participant's score in condition A with their score in condition B in a repeated measures design
• Counterbalancing controls order effects, it doesn't eliminate them
• Matched pairs design attempts to fix the problem with both participant variables in independent groups design and of order effects in repeated measures design