6.9 experimental design

Repeated measures

• the same participants complete both the conditions of the independent variable

• Produces related data

Evaluation

• order effects, may influence performance in the second condition. And may alter behaviour (demand characteristics

• This is controlled by ‘counter balancing’. One group does A then B. Other group does B then A

Independent groups design

• different participants complete a condition of the independent variable

• Randomly allocated to each condition (To avoid bias)

• Produces unrelated data

Evaluation

• participant variables - characteristics can influence the DV, extraneous variables which reduce validity

Matched pairs design

• Participants are assessed and ranked on a characteristic. Then the top two are randomly assigned to separated conditions, same for the next two etc…

• Produces related data. Scores in one condition can be paired with a data point in another condition

Evaluation

• reduced participant variables as they are matched on characteristics

• No order effects as they only take part in one condition

• Takes longer

• Needs twice as many participants

• There are still some participant variables that influence the DV