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 the independent groups design?

Answer 2

when participants are allocated to different groups where each group represents one experimental condition

Question 3

what are the strengths of the independent group design?

Answer 3

• order effects are not a problem
• participants are less likely to guess aims

Question 4

what are the issues with the independent group design?

Answer 4

• there are different participant variables
  > if a researcher finds a mean difference between the groups on the DV, this may be more to do with participant variables than the effects of the IV. these differences may act as a confounding variable, reducing the validity of the findings
• less economical than repeated measures as each participant contributes a single result only
  > twice as many participants are needed to produce equivalent data collected in a different design, thus increasing the time and money spent on recruiting participants

Question 5

what is the repeated measures design?

Answer 5

when all participants take part in all conditions of the experiment

Question 6

what are the strengths of the repeated measures design?

Answer 6

• participant variables are controlled
  > higher validity
• fewer participants are needed
  > less time spent recruiting them

Question 7

what are the issues with the repeated measures design?

Answer 7

order acts as a confounding variable

• order of the different tasks may be significant
  > counterbalancing is used to deal with this
• repeating 2 tasks could create boredom or fatigue that might cause deterioration in performance on the 2nd task
• participants’ performance may improve through the effects of practice, especially on a skill-based task
• demand characteristics tend to be more of a feature
  > more likely the participants will work out the aim of the study when they experience all conditions of the experiment

Question 8

what is the matched pairs design?

Answer 8

when pairs of participants are first matched on some variable(s) that may affect the DV. then one member of the pair is assigned to condition A and the other condition B
> it is an attempt to control for the confounding variable of participant variables

Question 9

what are the strengths of the matched pairs design?

Answer 9

order effects and demand characteristics are less of a problem

Question 10

what are the issues with the matched pairs design?

Answer 10

• participants can never be matched exactly, despite the attempt to reduce participant variables
• matching may be time-consuming and expensive, particularly if a pre-test is required, thus making it less economical than other designs