Experimental designs

• In independent groups design the participants in each condition are different. The groups/conditions are completely independent of each other. Participants are randomly allocated to each group/condition. Each group does only one condition of the experiment
• Strengths of IGD: Order effects not a problem as they take part in one condition
• Weaknesses of IGD: Individual differences between participants. Conditions have different participants and therefore may be a confounding variable affecting the results. Less economical - more participants needed which takes time to find plus 2 sets of materials
• Repeated measures design: each participant completes all conditions of the experiment, they are the same in a repeated measures design
• Strengths of RMD: Individual differences participants variables are controlled because the same participants do both conditions. Fewer participants are needed than IGD as they repeat the same conditions of the experiment
• Weaknesses of RMD: Order effects the result. Chance of demand characteristics. Using counter-balancing to try and overcome order effects. Half do A->B, half do B->A
• Matched pairs design: the participants in each group are carefully matched on important variables/characteristics that are relevant to the study, Then, for each matched pair, one goes into condition A and one into condition B. This is repeated for each pair
• Strengths of MPD: Order effects not a problem as only take part under one condition
• Weaknesses of MPD: Time consuming to match participants. Less economical than other designs. Even when matched carefully we can't control for every single variable. Even MZ twins will be slightly different in their behaviour
• Counterbalancing: a technique used to attempt to overcome the problem of order effects, which occurs in repeated measures design