experimental design

• Repeated measures design, every participant is tested on the same task multiple times, with the same conditions
• Independent group design each group of participants does one condition of the experiment, and the performance of the 2 groups is compared
• In matched pairs design two group of participants are used, but pairs are matched on key characteristics
• strengths of independent groups design

  • There are no order effects
  • Participants are less likely to guess the aims of the study (demand characteristics are eliminated
• Limitations of independent groups design

  • Different participants need to be recruited for each condition, which can be difficult and expensive.
  • There is a risk of participant variables (individual differences between participants) affecting the results between conditions, rather than solely manipulation of the independent variable.
• Strengths of Repeated measures design

  • The results will not be subject to participant variables (i.e. individual differences between participants), putting more confidence in dependent variable changes being solely due to manipulated changes in the independent variable.
  • As the same participants are used [at least] twice, extra participants do not need to be recruited.
• Limitations of Repeated measures design

  • There is risk of observing order effects (e.g. practice / fatigue effects, or demand characteristics), but this risk be reduced by counterbalancing (i.e. controlling the order of variables so that each order combination occurs the same number of times, e.g. one half of participants partake in condition A followed by B, whereas the other half partake in B followed by A).
  • If a participant drops out, data will be lost from all conditions of the experiment rather than one.
• Strengths of Matched Pairs design

  • Order effects will not be observed as participants only take part in one condition.
  • The tailored participant-matching process reduces the risk of participant variables (individual differences) from affecting results between conditions.
• Limitations of Matched Pairs design

  • Different participants need to be recruited for each condition, which is difficult and expensive.
  • Matching is a more complex process, and it will always be very difficult to match participants identically.