experi design

• The three types of experimental design

  1. independent groups
  2. repeated measures
  3. matched pairs
• Independent groups design: A design in which participants are randomly assigned to one of two experimental groups.
• Strengths of independent group design

  1. No order effects. Participants are only tested once so can't practise or become bored/tired. This controls an important confounding variable.
  2. Participants won't guess aims. Participants are only tested once so are unlikely to guess the research aims. Therefore, behaviour may be more 'natural'.
• Limitations of independent group design

  1. Participant variables. The participants in the two conditions are different, which act as extraneous variables and confounding variables. This may reduce the validity of the study.
  2. The design is less economical as the researcher need twice as many participants as repeated measures for the same data. This means there will be more time spent recruiting which is expensive.
• Repeated measures deign : A design in which participants are exposed to all conditions of an experiment. The order of conditions should be counterbalanced to avoid order effects.
• Strengths of repeated measures design

  1. Participant variables. The participants in the two conditions are the same, which controls an important confounding variable
  2. Fewer participants as there is half the number of participants needed than in independent groups. This means there will be less time recruiting which can save expenses.
• Limitations of repeated measures design 


  1. Order effects are a problem. Participants may be doing better or worse when doing a similar task twice. Also, there may be practice or fatigue effects. This reduces the validity of the results.
  2. Participants may guess aims which can lead to demand characteristics. This may reduce the validity of the results.
• Strengths of matched pairs design 


  1. Participant variables. The participants are matched on a variable that is relevant to the experiment. This controls participant variables and enhances the validity of the results.
  2. No order effects as participants are only tested once so they will have no practice and fatigue effects. This enhances the validity of the results.
• Limitation of matched pairs design

  
  

  1. Matching of participants is not perfect. Matching can be time-consuming and can't control all relevant variables. This means the researcher can't address all participant variables.
  2. More participants. Need twice as many participants as repeated measures for the same data. This means there is more time spent recruiting which is expensive.