Experimental Design

• Experimental design


  Refers to how the ppts are used in an experiment
• Independent Groups


  When two separate groups of participants experience two different conditions of the experiment as if there are two levels of IV in exp, all ppts can experience at least one level. Performance of the two groups is compared
• Strengths of independent groups

  Order effects are not a problem and ppts less likely to guess aim of experiment
• Limitations of independent groups

  Ppts in different groups aren't the same in ppt variables which may affect the DV- thus, it's a confounding variable affecting internal validity. Less economical as each ppt gives a single result, so more time/money spent of ppt recruitment- twice as many ppts needed to compare to RMs
• Repeated measures

  All ppts experience all conditions and guarantee that we compare 'like with like'
• Strengths of repeated measures

  Ppts variables are controlled and fewer ppts needed
• Limitations of repeated measures

  Order effects as ppts may be bored/fatigued causing deterioration in performance in 2nd task unless task is skill-based. Demand characteristics as ppts more likely to discover aims of study
• Matched pairs


  Ppts paired together on a variables or variables relevant to the exp. This is an attempt to control for CVs of ppt variables and often requires use of a pre-test if matching is to be effective
• Strengths of matched pairs

  Order effects and demand characteristics are less of a problem
• Limitations of matched pairs design

  Ppts will never be matched exactly and ppts will always have differences affecting the DV. More time-consuming and expensive especially if a pre-test is required