Experimental Designs

Question 1

What is an experimental design?

Answer 1

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

Question 2

What is an independant groups design?

Answer 2

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

Question 3

What is a repeated measures design?

Answer 3

• Where all participants take part in all conditions of the experiment

Question 4

What is a matched pairs design?

Answer 4

• Pairs of participants are first matched on some variables that may affect the dependant variable (e.g. similar iqs)
• Then one member of the pair is assigned to condition A and the other to condition B

Question 5

What is counterbalancing?

Answer 5

• An attempt to control for the effects of order in a repeated measures design
• Half the ppts experience conditions in one order & other half in opposite order

e.g. to counterbalance, researcher splits ppts into two groups:e.g.

Group 1 drinks caffeine first, then takes the reaction test, & later drinks decaf before taking the second test.
Group 2 drinks decaf first, takes the test, & later drinks caffeine before taking the second test.

Question 6

What is random allocation?

Answer 6

• An attempt to control participant variables in an independant groups design which ensures each ppts has same chance of being in one condition as any other

Question 7

What is one issue with an independant groups design?

Answer 7

• Independant groups are less economical than repeated measures as each ppts contributes a single result only.
• Twice as many participants would be needed to produce equivalent data to that collected in a repeated measures design
• This increases time/money spent on recruiting ppts

Question 8

What is one strength of independent groups?

Answer 8

• That order effects are not a problem whereas they are a problem for repeated measures desgins
• Ppts also are less likely to guess the aims

Question 9

What is the biggest issue for repeated measures?

Answer 9

• Each ppt has to do at least two tasks and the order of these tasks may be significant (i.e there are order effects)
• Order effects also arise because repeating two tasks could creat boredom or fatigue that might cause deterioration in performance on the second task so it matters what order the tasks are in.

Question 10

Give one strength for a repeated measures design.

Answer 10

• Participant variables are controlled because the same ppts take part in all conditions of the experiment (therefore higher validity)
• & Fewer participants are needed (therefore less time spnet recruiting them)

Question 11

What is the benefit of matched pairs?

Answer 11

• Ppts only take part in a single condition so order effects and demand characterisitcs are less of a problem

Question 12

What are the drawbacks of a matched pairs experimental design?

Answer 12

• Matching may be time consuming and expensive, particularly if a pre test is required
• So this is less economical than other designs