Why is matched pairs design better than independent groups?
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When conducting an experiment there are two main ways of allocating participants too different conditions. The most widely used designs are a repeated measures design or an independent measures design. In this blog I will be evaluating the pros and cons of both designs plus a third research design called matched pairs. Show An independent measures design assigns participants too separate groups. Each of the groups is then designated to a single research condition. This provides many advantages, for example the experiment has a high level of external validity because more participants are used in a study. Additionally individuals within each condition are less likely to be affected by order effects such as fatigue, history or maturation. An example of where these designs have been used in a study was Bandura, A., Ross, D. & Ross, S.A. (1961). The use of a independent measures design in this study helped because the children involved where less likely to get bored or distracted due to the fact they didn’t have to be involved in every single condition. However there are disadvantages to an independent measures design. For instance because different participants are used in every condition the effect of individual differences on the scores for each condition is much greater. This can result in inferences being made from studies where the results are in fact due to error from individual differences rather than the independent variable condition. Therefore every independent measures study can have problems with the internal validity of the results and the reliability of the results. In contrast to an independent measures design a repeated measures design has only one group of participants who complete every research condition. This is advantageous because fewer participants are needed to run an experiment. Additionally because the individuals in each condition are the same the study will have both greater internal validity and reliability. This design was implemented in Bartlett (1995) study War of the Ghosts. Bartlett’s study was researching the working memory and the use of the repeated measures design allowed for a way to easily measure changes in memory over time. While the repeated measures design has some distinct advantages it also has some major disadvantages. If participants drop out, this has a greater effect of the results of the experiment as a participant is effectively lost from each condition, rather than from only one condition. Additionally repeated measures designs can be affected by order effects, because participants are tested at different times. Order affects are such things as maturation and history which significantly decreases the internal validity of the experiment. There are also problems such as fatigue or practise affect, which only affect the second condition and bias the results. However these can be reduced by counterbalancing, which takes relatively little time and effort. To do this the order in which the participants complete the experiment is changed. Firstly the sample is split into two separate groups, group 1 and group 2. Group 1 completes the first condition (condition A) first and then the second condition (condition B). Whereas Group 2 completes the second condition (condition B) first and then the first condition (condition A). This procedure results in order effects being distributed across both conditions. The result of this is that they are similar for both groups and so balance the results out. There is also another research design called a matched pairs design which combines some of the qualities of both an independent and repeated measures design. A matched pairs design uses an independent measures design but the way in which individuals are allocated into a group is changed so that the results are less affected by individual differences. In this design participants are matched on a scale such as intelligence or personality. The aim of this process is too ensure the difference between the individuals within each of the groups is reduced. This means the results are more likely to be due to differences in the conditions rather than individual differences. In conclusion while both a repeated measures and independent measures design have advantageous qualities they also have many disadvantageous qualities. Whereas a matched pairs design has the best qualities of both designs. http://www.simplypsychology.org/experimental-designs.html http://www.holah.co.uk/page/experimental/ https://www.msu.edu/~henrikse/cep909/warofghosts.htm http://www.holah.co.uk/summary/bandura/ http://www.holah.co.uk/core-studies/ An independent measures design consists of using different participants for each condition of the experiment. The advantage of this is that there are no order effects, which is when participants behave differently due to the order of conditions performed, due to factors such as boredom or fatigue. However, the disadvantage of independent measures design is that there is the potential for error due to individual differences between the groups of participants. A repeated measures design consists of testing the same individuals on two or more conditions. The advantage of this is that individual differences between participants are removed as a potential confounding variable. Repeated measures also requires fewer participants, as data from all conditions is from the same group of participants. However, the disadvantages of repeated measures is that order effects can occur, and that the range of potential use is smaller than independent groups, as it is not always possible to test the same participants twice. Moreover, matched pairs design uses different participants for each condition, matching participants on key variables such as age, IQ, and gender. However, although this method combines the advantages of independent and repeated measures, it is an expensive and time consuming task. What are the advantages of matched pairs design?Now the two groups are matched in terms of both age and gender. Differences between the group means can no longer be explained by differences in age or gender of the participants. The primary advantage of the matched pairs design is to use experimental control to reduce one or more sources of error variability.
Why is repeated measures better than independent?The Benefits of Repeated Measures Designs
Further sample size reductions are possible because each subject is involved with multiple treatments. For example, if an independent groups design requires 20 subjects per experimental group, a repeated measures design may only require 20 total.
What are the disadvantages of independent groups design?You need twice as many participants so it is time consuming. Individual differences or participant variables may make the comparisons unreliable, so you can use random allocation which may balance it out as everyone has an equal chance of being selected for each condition.
What are some pros and cons of using independent group designs?Advantages of independent measures design include less time/money involved than a within subjects design and increased external validity because more participants are used. A disadvantage is that individual differences in participants can sometimes lead to differences in the groups' results.
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