Research Methods -> Design Of Experiments Flashcards
Independent groups design
This is where there are different participants in each group/condition. The participants only do the condition once, this avoids the problem that if all the participants did the test in both conditions any improvement in performance may be due to them having had a second opportunity to complete the task (which would be an extraneous variable).
Repeated measures design
This is where the same participants are used in each condition. The researcher can therefore compare the performances in each condition knowing that the differences weren’t due to participant variables. This allows for direct comparisons to be made without worrying about extraneous variables such as one group better than the other as would be the case in an independent groups design.
Matched-pair design
This is where there are different participants in each condition, but they are matched on important variables. This then allows comparisons to be made but without one group just being better than the other since the participants in each group have been matched with each other. A matched pairs design avoids order effects as well as less chance of demand characteristics.
Control groups
These are groups which have not experienced any of the manipulations of the IV that the experimental group might have. This allows the researcher to make a direct comparison between them in order to assess the impact of the IV.
Strengths of independent designs
No order effects.
Demand characteristics are less likely
Weaknesses of independent designs
Differences between people in each group may affect the results e.g. one group may just have a better memory
Strengths of repeated designs
Less chance of participant variables- because the same people do the test in all conditions any differences between individuals shouldn’t affect results.
Fewer participants are needed to get the same amount of data as opposed to an independent groups design.
Weakness of repeated designs
Order effects, any improvements in later conditions could be due to practice rather than due to the IV. Alternatively participants could perform worse due to fatigue or boredom.
Greater risk for demand characteristics as they are participating on more than one condition.
Strengths of matched designs
No order effects because the participants are only doing the condition once
Less chance of participant variables as important differences are minimised through matching
Weaknesses of matched designs
“Twice as many participants are required compared to repeated measures.
Time-consuming and can be difficult to find participants who match on key variables.”
Random allocation:
an attempt to control for participant variables in an independent groups design which ensures that each participant has the same chance of being in one condition or the other
Counterbalancing:
an attempt to control for the effects of order in a repeated measures design; half the participants experience the conditions in one order while the other half in the opposite order.
