Experimental designs

Question 1

Experimental design

Answer 1

The different ways in which participants can be organised in relation to the experimental conditions.

Question 2

Independent groups design

Answer 2

Participants are allocated to different groups where each group represents one experimental condition.

Question 3

Repeated measures design

Answer 3

All participants take part in all conditions of the experiment.

Question 4

Matched pairs design

Answer 4

Pairs of participants are first matched on some variables that may affect the dependent variable. Then one member of the pair is assigned to condition A and the other to condition B.

Question 5

Random allocation

Answer 5

An attempt to control for participant variables in an independent groups design which ensures that each participant has the same chance of being in one condition as any other.

Question 6

Counterbalancing

Answer 6

An attempt to control for the effects of order in a repeated measures design: half the participants experience the condition in one order, and the other half in the opposite order.

Question 7

What is a limitation of using an independent groups design?

Answer 7

• One is that the participants in the different groups are not the same in terms of participant variables.

Question 8

What is a second limitation of an independent groups design?

Answer 8

• Less economical than repeated measures as each participant contributes to a single result, whereas in a repeated measures design twice as many participants would be needed to collect equivalent data.
• This increases the time/money spent on recruiting participants.

Question 9

What is one strength of an independent groups design?

Answer 9

• Order effects are not a problem whereas they are a problem for repeated measures design.
• Participants are less likely to guess the aims.

Question 10

What is one limitation of a repeated measures design?

Answer 10

• Each participant has to do at least two tasks and the order of these tasks may be significant, so there are order effects.
• Order effects may also arise due to boredom or fatigue and could cause deterioration in performance on the second task or improvement through practice.

Question 11

What is a second limitation of a repeated measures design?

Answer 11

• Participants are more likely to work out the aims of the study so demand characteristics are more of a feature of repeated measures than independent groups.

Question 12

What is the two strengths of a repeated measures design?

Answer 12

• Participant variables are controlled so higher validity.
• Fewer participants are needed so less time spent recruiting them.

Question 13

What is a strength of a matched pairs design?

Answer 13

• Since they only take part in a single condition, order effects and demand characteristics are less of a problem.

Question 14

What is a limitation of a matched pairs design?

Answer 14

• Participants can never be matched exactly since there is some attempt to reduce participant variables.

Question 15

What is a second limitation of a matched pairs design?

Answer 15

• Matching may be time consuming and expensive particularly if a pre test is required so less economical then other designs.