Experimental designs

• Independent group design:


  when two separate groups of participants experience two different conditions of the experiment.
• Repeated measures:


  All participants experience both conditions of the experiment.
• Matched Pairs:


  Participants are paired together on a variable relevant to the experiment.
• Independent Groups:


  Those who occupy the different groups are not the same in terms of participant variables. These differences may act as a confounding variable, reducing the validity of the findings. To deal with this problem researchers use random allocation.
• Independent Groups:


  Less economical than repeated measures as each participant contributes a single result only. Twice as many participants would be required to produce equivalent data to that collected in a repeated measures design. This increases time/money spent.
• Independent Groups:


  Order effects are not a problem whereas they are in a repeated measures designs. Participants are less likely to guess the aims.
• Repeated measures:


  The order of tasks may be significant. (e.g. effects of energy drink may have a continuing effect on the water condition afterwards).
• Repeated Measures:


  Order effects are a problem because repeating two tasks could create boredom or fatigue that might decrease performance on the second task.
• Repeated Measures:


  Alternatively, participants' performance may improve through the effects of practice.
• Repeated Measures:


  Demand characteristics tend to be more of a problem as there is a higher chance of participants working out the aim of the study.
• Repeated Measures:


  The strengths are participant variables are controlled (therefore higher validity) and fewer participants are needed (less time spent recruiting them).
• Matched Pairs:


  Order effects and demand characteristics are less of a problem as participants only take part in one condition.
• Matched Pairs:


  Although there is some attempt to reduce participant variables in this design, participants can never be matched exactly. Even when identical twins are used as matched pairs, there will still be important differences between them that may affect the DV.
• Matched Pairs:


  Matching may be time-consuming and expensive, particularly if a pre-test is required, so this is less economical than other designs.