Experimental and research designs: repeated measures, independent groups and matched pairs, the issues with each and possible controls.
Experimental design describes the way participants are allocated to experimental groups of an investigation. Types of design include Repeated Measures, Independent Groups, and Matched Pairs designs.
Where different participants take part in each experimental condition (they will be allocated randomly).
Order effects cannot be observed, as no participants will be used in more than one condition.
Data collection will be less time-consuming if all conditions of the experiment can be conducted simultaneously.
Different participants need to be recruited for each condition, which can be difficult and expensive.
There is a risk of participant variables (individual differences between participants) affecting the results between conditions, rather than solely manipulation of the independent variable.
Where the same participants are allocated to all groups (i.e. take part in all conditions) of an experiment.
The results will not be subject to participant variables (i.e. individual differences between participants), putting more confidence in dependent variable changes being solely due to manipulated changes in the independent variable.
As the same participants are used [at least] twice, extra participants do not need to be recruited.
There is risk of observing order effects (e.g. practice / fatigue effects, or demand characteristics), but this risk be reduced by counterbalancing (i.e. controlling the order of variables so that each order combination occurs the same number of times, e.g. one half of participants partake in condition A followed by B, whereas the other half partake in B followed by A).
If a participant drops out, data will be lost from all conditions of the experiment rather than one.
Where participants take part in only one experimental condition, but they are recruited specifically to be similar in relevant characteristics (e.g. intelligence, gender, age) to ‘matched’ participants in the other condition(s).
Order effects will not be observed as participants only take part in one condition.
The tailored participant-matching process reduces the risk of participant variables (individual differences) from affecting results between conditions.
Different participants need to be recruited for each condition, which is difficult and expensive.
Matching is a more complex process, and it will always be very difficult to match participants identically.
Ethical issues such as lack of informed consent commonly arise, as deception is often required; debriefing, once the observation/experiment has ended, is necessary.
Explain one reason why Tobias used an independent groups design in his investigation. (2) October 2019
Explain one weakness of using a repeated measures design in this study. (2) June 2016
Describe why Kaleb chose to use an independent groups design for his investigation. (2) January 2017
Describe how Philippa could have used counterbalancing in her investigation. (2) October 2018
Explain one strength and one weakness of Cherry using a repeated measures design in her experiment. (4) January 2020
Explain one strength and one weakness of using an independent groups design. (4) October 2017
Explain one strength and one weakness of the investigation conducted by Helena. (4) October 2018
Explain one strength and one weakness of using a repeated measures design in Cha and Dao’s investigation. (4) October 2019