Experimental design

• What are the 3 experimental designs ?

  1. Repeated Measure Design
  2. Independent Groups Design
  3. Matched Pairs Design
• Repeated Measure Design - Limitation

  • Order of the conditions may affect performance
  • When participants do the 2nd part of the test they may guess the purpose of the experiment
• Repeated Measures Design - Method of dealing with these Limitations

  • Researcher may use 2 different tests to reduce a practise effect
  • The main way that order effects are dealt with is using counter balancing
• Repeated Measures Design


  All participants receive all levels of the IV
• Independent Groups Design

  • Participants are placed in separate (independent ) groups. Each group does one level of the IV
• Independent Groups Design Limitations

  1. The researcher cannot control the effects of participant variables
  2. Independent groups designs need more participants then repeated measures design in order to end up with the same amount of data
• Independent Groups Designs - Dealing with the limitations

  1. Randomly allocate participants to conditions which distribute variables evenly
• Matched Pair Designs

  • A compromise to use 2 groups of participants but match participants on key characteristics believed to affect performance on the DV
  • Then 1 member of the pair is allocated to the group A and the other to group B. The procedure is then the same as for independent groups
• Matched Pairs Designs - limitations

  1. Time consuming
  2. Its not possible to control all participant variables
• Matched Pairs Designs - dealing with the limitations

  1. Restrict the number of variables to match on to make it easier
  2. Conduct a pilot study to consider key variables that might be important when matching