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

Question 11

how can the problem of participant variables in an independent groups design be addressed?

Answer 11

• participants should be randomly allocated to the different experimental conditions
• random allocation attempts to evenly distribute participant characteristics across the conditions of the experiment using random techniques

Question 12

how can counterbalancing be used in an attempt to control order effects in a repeated measures design?

Answer 12

• half the participants take part in condition A then then B, the other half take part in condition B then A
• as with random allocation, counterbalancing does not remove or prevent the problem, but attempts to balance out the effects