Are single case designs effective?

Deciding whether a case study or a single case study design is the best to use in research depends utterly on what type of results and findings your trying to find out. Single-subject designs are most often used in psychology and are sensitive towards individual differences unlike group case studies, which are more sensitive to the averages of groups. In single-subject designs each participant serves as his or her own control, which is similar to a time-series design.

Single case studies use a continuous assessment therefore the behavior of the individual is observed repeatedly over time. This insures that any treatment effects or changes that occur to the individual are a result of the treatment over time. Where case studies often test two different groups and compare the differences before and after the treatments.

McMillan (2004) summarized five characteristics of single-subject research. It is key that it’s a reliable measure as it involves multiple measures. Also conditions such as time of day and location should be kept constant over measures, especially for before and after treatments. Also as the same measure is repeated over and over again it is vital that it’s a repeated measurement. Repeated measurements ensure a clear pattern of consistency in the behavior over time. McMillan also added that descriptions of conditions should be detailed in description. He also added that baseline and treatment conditions were important. The baseline behavior provides ‘the frame of reference which future behavior is compared’. It’s important to do follow the single-variable rule with a single subject design.

Where the pros of a single case study are mentioned above case studies have advantages of their own. From a good case study in psychology it’s possible for the development of hypotheses for later testing and a case study can provide detailed descriptions of specific cases. Although saying this, case studies in psychology can often be hard draw a cause and effect relationships or test hypotheses.

Therefore I believe the use of case study or a single-case study depends on what type of data is collected (qualitative or quantitative) and what conclusion the researcher is trying to reach.

McMillan, J. H. (2004). Educational Research: Fundamentals for the Consumer, 4th Edition. Allyn and Bacon: Boston.

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8 thoughts on “Are single case designs effective?

  1. Hello! Really good blog! 🙂 I would just like to add that single case studies can be extremely useful to study extraordinary phenomena as well. Such as Phineas Gage (http://mindhacks.com/2008/05/21/psychologys-greatest-case-studies/) or other cases where the brain has been damaged to study the resulting behaviour. As it would be a little bit unethical to make participants undergo these types of experience purposefully! 🙂 Look forward to reading your next blog.

  2. Good informative blog! You have explained single case designs and their pros very well but haven’t really balanced the argument with many of it’s cons. Although I agree that they can be very useful when wanting to collect rich data over time, and study rare events of individuals (e.g. Phineas Gage); this can be very helpful when wanting to localise function and support theory – in my example’s case personality and language are localised in the frontal lobes. However, without other cases like this we cannot say for sure that if a steal rod went through anybody else’s head, that they would suffer the exact same consequences that Phineas Gage did due to individual differences. This is why single subject designs have low external vality. Case studies have poor internal validity and therefore it’s hard to generate a causal relationship and there is often bias in observers and the interpretation of the data.

  3. I agree with the person above that there could be more discussion of cons but I fell that single subject designs are never really discussed during our research modules. Still they are an important type of methodology and you did discuss some of the pros. SSD are also a very useful methodolgy if you wish to carry out a longitudinal study which can be highly benificial especially in psychological areas such as developmental.

    However all case studies firstly require a lot of time, money and commitment. They are also vastly subjective and hard to quantify and find statisitcal significance. Your also a bit lost if your particpant decides to withdraw from the research and any results you do draw cannot really be generalised unless you carry out lots more case studies into the same area.

    However these weaknesses may not be as apparent when the case study is being used to investigate areas where the population itself is very small i.e. a specific disease/disorder. In these cases case studies are often the most approriate method and can provide us with a worth of information on often a previously misunderstood topic.

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  5. Nice blogging.. I think single case studies are very effective as-well especially when investigating new ideas, it is normally from these deeply studied new ideas that bigger ideas appear that can then be tested using perhaps quantitative methods, which you can then use to draw inferences.

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  7. Having figured out the actual difference between the two designs case study and single subject design, i would like to correct my previous comment in which i was talking about case studies not single case designs. However, my opinion still stands i think single case designs are effective, more effective than case studies simple because you get the whole deal with a single case design, the detailed description of the subject as well as a causal relationship. Its all okay to just know the behavior of of an individual but to be able to intervene and see a behavior change as a result of the intervention (you would have to do a few repetitions to be sure of the casual effect) is what you want from a study.

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