Experimental designs Flashcards
What does experimental designs mean?
Refers to the way in which participants are used in experiments
What is an independent groups design?
An independent groups design is when two separate groups of participants experience two different conditions of the experiment. If there are two levels of the independent variable (IV) this means that all participants experience one level of the IV only.
The performance of the two groups would then be compared.
What is a strength of independent groups?
No order effects
- They are a problem for repeated measures designs. Participants are also less likely to guess the aims.
What are 2 limitations of independent groups?
Participant variables
- Participants who occupy the different groups are not the same. If a researcher finds a mean difference between the groups on the dependent variable (DV) this may be more to do with individual difference (participant variables) than the effects of the IV. To deal with this problem researchers use random allocation.
Less economical
- Independent group designs are less economical than repeated measures as each participant contributes a single result only. Twice as many participants would be needed to produce equivalent data to that collected in a repeated measures design.
What is a repeated measures design?
Repeated measures is when all participants experience both conditions of the experiment.
Each participant would experience condition A (the experimental condition).
Each participant would then later be tested again in condition B (the control condition).
Following this, the two sets of data from both conditions would be compared to see if there was a difference.
What is a strength of repeated measures?
Participant variables controlled
- Participant variables are controlled and fewer participants are needed as you are using the same participants for both conditions
What are 2 limitations of repeated measures?
Order effects
- each participant 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 create boredom or fatigue that might cause deterioration in performance on the second task.
Demand characteristics
- It is likely participants will work out the aim of the study when they experience all conditions of the experiment. For this reason, demand characteristics tend to be more of a feature of repeated measures designs than independent groups.
How can researchers deal with order effects?
Counterbalancing - the way of controlling the impacts of order effects. The ABBA effect
What is a matched pairs design?
Participants are paired together on a variable or variables relevant to the experiment. For instance, in a memory study participants might be matched on their IQ, as this might be a good indicator of their ability to recall information. The two participants with the first and second highest IQ scores would be paired together. Then one participant from each pair would be allocated to a different condition of the experiment. This is an attempt to control for the confounding variable of participant variables and often necessitates the use of a pre-test if matching is to be effective.
What is a strength of matched pairs?
Order effects and demand characteristics controlled
- Participants only take part in a single condition so order effects and demand characteristics are less of a problem.
What are 2 limitations of matched pairs?
Participant variables
- Although there is some attempt to reduce participant variables in this design, participants can never be matched exactly. This may effect the DV.
Less economical
- Matching may be time-consuming and expensive, particularly if a pre-test is required, so this is less economical than other designs.
