Experimental design

Question 1

Independent groups

Answer 1

One group does condition A and a second group does condition B

(participants should be randomly allocated to experimental groups)

Question 2

Independent groups AO3

Answer 2

+ No order effects: participants are only tested once so can’t practise or become bored/tired, this controls an important confounding variable

+ Won’t guess the aim: participants only tested once so are unlikely to guess the research aims, therefore behaviour may be more ‘natural’ (higher realism)

• Participant variables: the participants in the two groups are different, acting as extraneous variables and confounding variables, may reduce the validity of the study
• Less economical: need twice as many participants as repeated measures for same data, more time spent recruiting which is expensive

Question 3

Matched pairs

Answer 3

Two groups of participants are used but they are also related to each other by being paired in participant variables that matter for the experiment

Question 4

Matched pair AO3

Answer 4

+ Participant variables: participants matched on a variable that is relevant to experiment, this controls participant variables and enhances the validity of the results

+ No order effects: participants are only tested once so no practice or fatigue effects, this enhances the validity of the results

• Matching is not perfect: time-consuming and can’t control all relevant variables, cannot address all participant variables
• More participants: need twice as many participants as repeated measure for same data, more time spent recruiting which is expensive

Question 5

Repeated measures

Answer 5

Same participants take part in all conditions of an experiment

The order of conditions should be counterbalanced to avoid order effects

Question 6

Repeated measure AO3

Answer 6

+ Participant variables: the person in both conditions has the same characteristics, this controls an important CV

+ Fewer participants: half the number of participants is needed than in independent groups, less time spent recruiting participants

• Order effects are a problem: participants may do better or worse when doing a similar task twice. Also practice and fatigue effects, reduced the validity of the results
• Participants guess aims: participants may change their behaviour, this may reduce the validity of the results