Experimental Design Flashcards
What is experimental design?
The way in which participants are allocated to conditions.
What are the 3 types of experimental design?
Independent groups.
Repeated measures.
Matched pairs design.
What is an independent groups design?
Different groups in each condition.
Participants randomly allocated to each group.
State two advantages of an IGD.
No order effects:
As different participants do each condition there are no order effects whereby the order in which the conditions are done may have an effect on the outcome.
Demand characteristics:
Participants do one condition each; therefore there is less chance that they can guess the purpose of the study and act accordingly.
Time saved:
Both sets of participants can be tested at the same time, saving time and effort.
State two disadvantages of an IGD.
More participants needed:
With participants each doing only one condition, twice as many participants as needed as for a repeated measures design (RMD).
Group differences:
Differences in results between the two conditions may be due to participant variables (individual differences) rather than manipulations of the IV.
For example, participants in one condition may be more intelligent than those in another condition.
This is minimised by random allocation of participants to each condition.
What is a repeated measures design?
Each participant is tested in all conditions of an experiment.
Participants are therefore being tested against themselves.
State two advantages of an RMD.
Group differences:
As the same people are measured in all conditions, there are no participant variables (individual differences) between the conditions.
More data/fewer participants:
As each participant produces two or more scores, more data is produced compared with an independent measures design (IMD).
Therefore fewer participants are needed to get the same amount of data.
State two disadvantages of an RMD.
Order effects:
With a RMD, participants do all conditions and the order in which they do these conditions can affect the results.
Participants may perform worse in the second condition due to fatigue or boredom (negative order effect) or perform better due to practice or learning (positive order effect).
Counterbalancing can control this, where half the participants do Condition A followed by Condition B, and the other half do Condition B and then Condition A.
Demand characteristics:
By participating in all conditions, it is more likely that participants may guess the purpose of the study and act accordingly.
Takes more time:
A gap may be needed between conditions to counter the effects of fatigue or boredom.
Each condition may also need different materials; for example, in a memory test the same list of words could not be used for both conditions.
What is an ABBA design?
A method used in RMD.
The first half of the group (group a), experiences condition b.
Then the other half of the group (group b), experiences condition a.
What is a matched pairs design?
A type of RMD.
Each participant is only in one group, like in an independent groups design.
Participants in two groups are matched for some relevant factor that you want to measure (intelligence, gender, etc.)
State two advantages of an MPD.
No order effects:
As different participants do each condition there are no order effects.
Demand characteristics:
Participants do one condition each; therefore there is less chance of them guessing the purpose of the study.
Group differences:
As participants are matched, there should be less chance of participant variables (individual differences) affecting the results.
State two disadvantages of an MPD.
More participants:
With participants each doing only one condition, more participants are needed than for an RMD.
Matching is difficult:
It is impossible to match all variables between participants and an unmatched variable might be vitally important.
Also, even two closely-matched individuals will have different levels of motivation or fatigue at any given moment in time.
Time-consuming:
It is a lengthy process to match participants.
What are control groups?
In some experiments, one of the groups is used to provide baseline information.
One group receives the experimental treatment (alteration of IV).
The other group, the control group, acts as a comparison to the experimental group to study the effects
