Repeated measures design

• One single group of people perform all of the conditions of the experiment.
• A comparison is made between a single participants score on one condition to their score on other condition.
• (+) No participant variables (an EV) as same participants used in both conditions
• (+) Fewer participants are needed which makes the design more economical.
• (-) Demand characteristics likely as both conditions are seen which affects validity
• (-) Potentially could be order effects, confounding the results and making them invalid (e.g. may do better on the second condition due to the practice effect or being less anxious OR may do worse on the second condition due to the boredom effect)
• Order effects

  The fact that the order the participants complete the conditions (in a RM design) could affect results.

  INCLUDES:

  Practise Effects – They could just get better in the second condition as they have practised the task

  Fatigue Effects – They could get bored in second condition as they have done the task once already.
• Dealing with order effects in a

  repeated measures design

  Counterbalancing AKA The ‘ABBA’ method

  Way 1: AB or BA

  Divide participants into two groups:

  Group 1: each participant does A and then B

  Group 2: each participant does B and then A

  So any order effects will cancel each other out (or both conditions will be subject to them)
• Way 2: ABBA

  All participants take part in each condition twice:

  Trial 1: Condition A

  Trial 2: Condition B

  Trial 3: Condition B

  Trial 4: Condition A

  Then compare scores on trials 1 and 4 with trials 2 and 3.

  Again, so any order effects will cancel each other out (or both conditions will be subject to them)