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Experimental Designs (the way in which participants are allocated to the…
Experimental Designs
the way in which participants are allocated to the different conditions in an experiment. There are 3 experimental designs : Repeated Measures, Independent Groups and Matched Pairs :
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All participants take part in all conditions = one group of participants completes one condition then the same group completes the next condition
Advantages
No Participant Variables No individual differences between the participants in each condition. I.E. participants in condition A will not differ in any ways fro those in condition B as they are the same participants. Positive because it increases the internal validity of the research
Requires Half the Number of Participants as other Designs Less participants needed in comparison to independent groups / matched pairsto achieve the same amount of data. For example, to achieve 10 participants in each condition, RM only needs that 10 - compared to 20 needed for other designs. Positive as it means studies using this design do not have to recruit as many participants which is cheaper and less time-consuming.
Disadvantages
Suffer from Order Effects the order participants complete the different conditions may affect their performance. E.g. participants may do better in the second test because they have already had practice at the task (practice effect) or may do worse because they are bored with doing the same task again (boredom effect). Problem as it would lower the internal validity of the research.
High Demand Characteristics participants have more of a chance of guessing the aim of the experiment which might affect their behaviour. For example, completing a memory task in noisy conditions and then in silence, participants may work out what you are expecting to achieve and change their behaviour accordingly. Problem as it reduces the study’s internal validity.
Participants are placed into separate (independent) groups. Each group completes one condition of the experiment only. We then compare the performance (DV) of each group.
Disadvantages
Low Degree of Control over Participants Variables there might be individual differences between the participants in each condition that have not been controlled and could unfairly influence the results. E.g. participants in condition A may be, on average, much more intelligent than those in condition B. Problem because it decreases the validity of the research and may confound the results.
Requires Twice as Many Participants as a Repeated Measures Design more participants are needed with this design to achieve the same amount of data. For example, to achieve 10 participants in each condition, 20 participants are needed in total compared only 10 being needed for a repeated measures design. Negative as it means studies using this design have to recruit more participants which is more effort and more time-consuming
Advantages
Does NOT Suffer from Order Effects
the order participants complete the different conditions does not affect performance because participants only complete one condition. E.g. participants will not do better (practice effect) or worse (boredom effect) in the second task because they only complete one task. Positive as it increases the internal validity of the research.
Low Demand Characteristics participants have less of a chance of guessing the aim of the experiment. E.g. as participants only take part in one condition, they are not necessarily aware of the research expectations so their behaviour is less likely to change to fit in with these expectations. Positive as it increases the study’s internal validity.
Different participants are used in each condition. HOWEVER, the participants have been matched into pairs based on important characteristics that may influence the results.
Advantages
Does NOT Suffer from Order Effects
the order participants complete the different conditions does not affect performance because participants only complete one condition. E.g. participants will not do better (practice effect) or worse (boredom effect) in the second task because they only complete one task. Positive as it increases the internal validity of the research.
Low Demand Characteristics participants have less of a chance of guessing the aim of the experiment. E.g. as participants only take part in one condition, they are not necessarily aware of the research expectations so their behaviour is less likely to change to fit in with these expectations. Positive as it increases the study’s internal validity.
Disadvantages
Low Degree of Control over Participants Variables although participants have been matched on important criteria to control participant variables more than an independent group design - there is still more chance of individual differences between the participants in each condition than a RM design that could still unfairly influence the results. E.g. participants in condition A may be, on average, much more intelligent than those in condition B. Problem because it decreases the validity of the research and may confound the results.
Requires Twice as Many Participants as a Repeated Measures Design more participants are needed with this design to achieve the same amount of data. For example, to achieve 10 participants in each condition, 20 participants are needed in total compared only 10 being needed for a repeated measures design. Negative as it means studies using this design have to recruit more participants which is more effort and more time-consuming.