Experimental Design

Matched Pairs Design

using different but similar participants in each condition of an experiment. An effort is made to match the participants in each condition on characteristics that might affect performance

Repeated Measures Design

using the same participants in each condition of an experiment

Independent Groups Design

using different participants for each condition of the experiment

Advantages of the Matched Pairs Design

• Participant variables are kept constant between conditions

• Demand characteristics are less of a problem as the participants only participate in one condition, so is naïve to the test, and is less likely to guess the aim of the study

Disadvantages of the Matched Pairs Design

• Participant variables can never be perfectly matched in every aspect, also matching participants is very time consuming and difficult

• More participants are required and therefore is less economical

Advantages of the Repeated Measures Design

• Fewer participants are required so it’s therefore more economical

• Participant variables which could become extraneous variables are kept constant between condition since the same participants are used in both conditions

Disadvantages of the Repeated Measures Design

• Order effects such as learning, fatigue and boredom may become constant errors when one condition is done after another e.g. a participant given the same test may do better due to practice

• Demand characteristics may become a problem. As the participant does both conditions of the experiment, they have more clues to pick up on and may ‘guess’ the aim’

Advantages of the Independent Groups Design

• Order effects don’t occur since the participant only participates in one condition

• Demand characteristics are less of a problem this is because participants are matched and then only take part in one condition

• Order effects such as learning, fatigue or boredom don’t influence a second condition since the participant only participates in one condition

Disadvantages of the Independent Groups Design

• More participants are required and therefore it is less economical

• Participant variables differ, which could act as extraneous variables unless controlled - participant variables may affect the results

What is a method of dealing with the limitations of the Independent Groups Design?

Randomly allocate participants to conditions which distribute participant variables evenly.

What is a method of dealing with the limitations of the Repeated Measures Design?

Counterbalancing, alternate the order in which participants do the conditions of the experiment to average out order effects.

What is a method of dealing with the limitations of the Matched Pairs Design?

Restrict the number of variables to match on to make it easier. Conduct a pilot study to consider key variables that might be important when matching.