Experimental Design

Question 1

Repeated Measures Design

Answer 1

Each PP takes part in every condition being tested.

Each condition represents one level of the IV

Question 2

Independent Groups Design

Answer 2

Different PP are allocated to two or more experimental groups representing different levels of the IV.

Question 3

Matched Pairs Design

Answer 3

PP who are similar on key variables are paired. The people in each pair are placed in separate groups.

Question 4

RM +/-

Answer 4

+ Good control of PP variables as the same person is tested twice.

+ Fewer PP needed.

• Order effects produced. A PP may be better on the second test as they are getting better with experience (practice effect), or may perform worse due to boredom (fatigue effect).
• PP may guess the purpose of experiment as they do both conditions (demand characteristics).

Question 5

IG +/-

Answer 5

+ Avoids order effects because each PP is only tested once.

+ Avoids participants guessing the aims of experiment.

• No control of PP variables.
• Needs more PP than RM design.

Question 6

MP +/-

Answer 6

+ Controls for PP variables because of the matching.

+ Avoids order effects.

• Very time consuming to match PP on key variables.
• May not control all PP variables because you can only match on variables known to be relevant.

Question 7

Counterbalancing

Answer 7

Deals with order effects.

Do this by changing order of conditions so that:
- Half the PP receive condition A first followed by B.

• Half the PP receive condition B first followed by A.

Acts as a counterbalance as people doing condition A last will benefit from practice effects but an equal number of those doing B last will also benefit.

Ensures each condition is tested first or second in equal amounts.

Question 8

Randomisation

Answer 8

Controls PP variables in IG.

Do this by deciding who goes in each group randomly, so the two groups should be similar.