RM - Experimental design Flashcards
What is a comparison condition?
A condition where there are different levels of the IV.
What is counterbalancing?
An experimental technique used to overcome order effects when using a repeated measures experimental design. Ensures that each condition is tested first or second in equal amounts.
What is the experimental design?
A set of procedures used to control the influence of factors such as participant variables in an experiment.
What is independent group design?
Participants are allocated to two or more groups representing different levels of the IV, usually by random allocation techniques.
What is the matched pairs design?
Pairs of participants are matched on key variables such as age or IQ. One member of each pair is randomly allocated to each experimental condition.
What is the order effect?
In a repeated measure design, an extraneous variable arising from the order in which conditions are presented, e.g. a practise effect or fatigue effect.
What is random allocation?
Allocating participants to experimental conditions or groups using random techniques.
What is the repeated measures design?
Each participant takes part in every condition under test i.e. each level of the IV.
What happens the repeated measures design?
All participants receive all levels of the IV and then we compare the performance (DV) of the participant on the two tests.
What are the limitations of the repeated measures design?
The order of the conditions may affect the performance (an order effect). For example, people may do better on the second test if they were nervous on the first or because of practice effect. Or they may be bored by the time they do the second test.
When participants do the second test they may guess the purpose of the experiment, which may affect their behaviour. For example, some participants may purposely do worse on the second test because they want it to appear as if they work less well in the afternoon.
How can you deal with the limitations of the repeated measures design?
Researchers may use 2 tests to reduce the practice effect (though they must be equivalent).
Order effects dealt with using counterbalancing.
In order to stop the participants guessing the aims of a study, a cover story can be presented about the purpose of the test.
What happens the independent groups design?
Participants are placed in separate groups where each group does one level of the IV. We compare the performance (DV) of the 2 groups.
What are the limitations of the independent groups design?
Researcher can’t control the effects of participant variables (i.e different abilities/characteristics).
Needs more participants than repeated measures design in order to end up with the same amount of data.
How can you deal with the limitations of the independent groups design?
Randomly allocate participants to conditions which (theoretically) distribute participant variables evenly.
Random allocation can be done by placing names in a hat and drawing them out so that every other person goes into group A
What happens the matched pairs design?
A compromise is to use two groups of participants but match participants on key characteristics believed to affect performance on the DV.
Then one member of the pair is allocated to Group A and the other to group B. The procedure is then the same as for independent groups.
The characteristics matching must be relevant to the study e.g. you don’t need to match genders if you were testing memory unless there was some evidence that gender was a potential confounding variable.
What are the limitations of the matching pairs design?
Time consuming and difficult to match participants on key variables as the researcher probably has to start with a large group to ensure they can obtain matched pairs on key variables.
It is not possible to control all participant variables as you can only match on variables known to be relevant, but it could be that others are important. E.g. in a memory experiment you might match on memory abilities but later find out that some of the participants had been involved in a teaching programme to boost memory skills and you should have matched on this.
It is not possible to control all participant variables as you can only match on variables known to be relevant, but it could be that others are important. E.g. in a memory experiment you might match on memory abilities but later find out that some of the participants had been involved in a teaching programme to boost memory skills and you should have matched on this.
Restrict the number of variables to match on to make it easier.
Conduct a pilot study to consider key variable that might be important when matching.
How do you counterbalance order effects?
When two conditions (A and B):
Way 1: AB or BA
- Divide participants into 2 groups.
- Group 1: each participant does A then B.
- Group 2: each participant does B then A.
Way 2: ABBA
- All participants take part in each condition twice.
- Trial 1: Condition A (morning).
- Trial 2: Condition B (afternoon).
- Trial 3: Condition B (afternoon).
- Trial 4: Condition A (morning).
Then compare score on 1 and 4 with 2 and 3.
