Experimental Design and Counterbalancing

3 main experimental designs

Repeated measures

Independant groups

Matched pairs

Explain repeated measures

All participants take part in both condtions of the experiment

Explain independant groups

All participants are allocated to different groups

where each one represents one experimental condition

Explain matched pairs design

Pairs of participants are first matched one some variables that may effect the DV

Then one member of the pair is assigned to either condition A or B

Explain counterbalancing

An attempt to control for the effects of repeated measures design

Half the participants experience ½ of the conditions then vice versa

Strengths of a repeated measures design

• controlled variables

• fewer participants are needed

Limitations of an RM

• order effects

(each participant is doing the task 2 times, they can also become bored and fatigued, or their skills will be improved)

• demand characteristics

Strengths of a independant groups design

• no order effects

• no demand chacteristics

Limitations of independant groups design

• results may be due to induvidual differences 

• less economical

How do investigators deal with the limitations of a IG study

Use random allocation so induvidual differences don’t effect results

Strengths of a MP

• no order effects

• no demand characteristics