•           In a repeated measures design, each individual participates in each condition of the experiment.

•           Why Researchers Use Repeated Measures Designs:

–          researchers don’t have to worry about balancing individual differences across conditions of the experiment because all participants are their own control.

–          these designs require fewer participants,

–          they are convenient and efficient, and

–          repeated measures designs are more sensitive.

•           A “sensitive” experiment is one that can detect the effect of the independent variable, even when that effect is small.

•           The main disadvantage of repeated measures designs is practice effects.

•           Practice effects arise because people change as they are repeatedly tested.

–          As participants complete the dependent variable measures after each condition, they may get better with practice, or they may become tired or bored.

•           Practice effects must be balanced, or averaged, across the conditions of the experiment.

•           Counterbalancing the order of the conditions makes sure that the practice effects are distributed equally across the conditions of the experiment.

•           Practice effects can’t be eliminated, but they can be balanced, or averaged, across the conditions of an experiment.

•           ABBA Counterbalancing

–          Present the conditions of the experiment in one sequence followed by the opposite of that sequence.

–          ABBA counterbalancing balances practice effects only when practice effects are “linear.”

–          Linear practice effects occur when participants change in the same way following each presentation of a condition.

–          Nonlinear practice effects occur when participants change dramatically following the administration of a condition.

•           This can occur when participants experience an insight regarding how to complete the experimental task during the course of the experiment.

•           May happen through:

o          Participants having a slow start with erratic or no pattern to practice effects in beginning

o          Participants having a sudden jump in practice effects

o          Participants reaching a plateau in the pattern of practice effects

                Problem of Differential Transfer

•           When should repeated measures designs not be recommended?

–          When differential transfer is possible.

–          This occurs when the effects of one condition persist and affect participants’ experiences during subsequent conditions.

–          Researchers can assess whether differential transfer is a problem in their research by comparing the results for their independent variable when tested in a pilot study using a random groups design and when tested in a repeated measures experiment.