The former, for example, would examine only the overall nature of an international organization, whereas the latter would also look to specific departments, programmes, or policies etc.
One of the principal reasons for this, he argues, is the relationship between the use of case studies in social research and the differing epistemological traditions — positivist, interpretivist, and others — within which it has been utilised. Philosophy of science concerns are obviously a complex issue, and beyond the scope of much of this paper. That said, the issue of how it is that we know what we know — of whether or not a single independent reality exists of which we as researchers can seek to provide explanation — does lead us to an important distinction to be made between so-called idiographic and nomothetic case studies Gerring, b.
The former refers to those which purport to explain only a single case, are concerned with particularisation, and hence are typically although not exclusively associated with more interpretivist approaches. The latter are those focused studies that reflect upon a larger population and are more concerned with generalisation, as is often so with more positivist approaches[2]. The importance of this distinction, and its relation to the advantages and limitations of single case study analysis, is returned to below.
Thirdly, in methodological terms, given that the case study has often been seen as more of an interpretivist and idiographic tool, it has also been associated with a distinctly qualitative approach Bryman, If case studies can reliably perform any or all three of these roles — and given that their in-depth approach may also require multiple sources of data and the within-case triangulation of methods — then it becomes readily apparent that they should not be limited to only one research paradigm.
Exploratory and descriptive studies usually tend toward the qualitative and inductive, whereas explanatory studies are more often quantitative and deductive David and Sutton, It is perhaps better to think of case studies as transparadigmatic; it is mistaken to assume single case study analysis to adhere exclusively to a qualitative methodology or an interpretivist epistemology even if it — or rather, practitioners of it — may be so inclined.
Having elucidated the defining principles of the single case study approach, the paper now turns to an overview of its main benefits. As noted above, a lack of consensus still exists within the wider social science literature on the principles and purposes — and by extension the advantages and limitations — of case study research.
Eckstein proposed a taxonomy which usefully identified what he considered to be the five most relevant types of case study. As opposed to the opportunity this presented primarily for theory application, Eckstein identified heuristic case studies as explicit theoretical stimulants — thus having instead the intended advantage of theory-building.
So-called p lausibility probes entailed preliminary attempts to determine whether initial hypotheses should be considered sound enough to warrant more rigorous and extensive testing. As a subset of the latter, however, Jack Levy notes that the advantages of idiographic cases are actually twofold.
Secondly, they can operate as theory-guided case studies, but ones that seek only to explain or interpret a single historical episode rather than generalise beyond the case. Harnessing various methods, process tracing may entail the inductive use of evidence from within a case to develop explanatory hypotheses, and deductive examination of the observable implications of hypothesised causal mechanisms to test their explanatory capability[4].
It involves providing not only a coherent explanation of the key sequential steps in a hypothesised process, but also sensitivity to alternative explanations as well as potential biases in the available evidence Bennett and Elman John Owen , for example, demonstrates the advantages of process tracing in analysing whether the causal factors underpinning democratic peace theory are — as liberalism suggests — not epiphenomenal, but variously normative, institutional, or some given combination of the two or other unexplained mechanism inherent to liberal states.
Within-case process tracing has also been identified as advantageous in addressing the complexity of path-dependent explanations and critical junctures — as for example with the development of political regime types — and their constituent elements of causal possibility, contingency, closure, and constraint Bennett and Elman, b. Bennett and Elman also identify the advantages of single case studies that are implicitly comparative: deviant, most-likely, least-likely, and crucial cases.
Of these, so-called deviant cases are those whose outcome does not fit with prior theoretical expectations or wider empirical patterns — again, the use of inductive process tracing has the advantage of potentially generating new hypotheses from these, either particular to that individual case or potentially generalisable to a broader population. A classic example here is that of post-independence India as an outlier to the standard modernisation theory of democratisation, which holds that higher levels of socio-economic development are typically required for the transition to, and consolidation of, democratic rule Lipset, ; Diamond, Conversely, if a theory cannot pass a most-likely case, it is seriously impugned.
Single case analysis can therefore be valuable for the testing of theoretical propositions, provided that predictions are relatively precise and measurement error is low Levy, As Gerring rightly observes of this potential for falsification:.
From various epistemological and analytical standpoints, single case study analysis can incorporate both idiographic sui generis cases and, where the potential for generalisation may exist, nomothetic case studies suitable for the testing and building of causal hypotheses. As shown in Fig. A return toward baseline levels of performance occurred when treatment was withdrawn. ABA design strategy used by Renvall et al.
Naming performance on trained and control items during A phases of the study and that on trained items during the B treatment phase is shown. Reprinted with permission. A frequently used alternative to the A—B—A—B design is the multiple baseline design across behaviors, which does not require returns to baseline levels of responding to demonstrate internal validity. This design, in essence, is a series of A—B designs. Baseline data are collected on two or more independent behaviors in each study participant.
Following this, the independent variable is applied to one behavior at a time during the B phase, while the A phase is continued for the remaining behaviors under study. When a treatment effect is established for the first behavior, treatment is extended to the second behavior, and so on, until all behaviors have been individually treated.
Experimental control is demonstrated in this design when changes in the dependent variable s occur only when the B phase is in effect for each behavior; baseline performance of untreated behaviors remains stable, until treated. Like the A—B—A—B design, the multiple baseline strategy allows replication of the treatment effect within subjects, i. Across subject replication is established by entering more than one participant into the study. Because the multiple baseline design requires sequential application of treatment to separate behaviors order effects must be ruled out.
Thus, application of treatment to the behaviors under investigation must be counterbalanced across participants and the number of participants required for a particular study is dependent on the number of behaviors studied. Take for example, a study examining the effects of treatment on naming.
The experimenter decides to study three sets of words, with each set tested in baseline and sequentially trained. To rule out order effects in such a study, the order of training each word set must be counterbalanced; thus three participants are required, with each receiving a different treatment order.
For full replication in such a study, each order requires replication in an additional participant, thus a multiple baseline design across behaviors with three behaviors requires six participants. Another issue relevant to the multiple baseline design across behaviors is that the behaviors must be functionally independent and, at the same time, amenable to the treatment under investigation.
This means, for example in a naming study using three sets of words, that training one set of words would have no effect on the untreated sets. If the behaviors are not functionally independent, treatment of one set may influence the others, i. While such an effect is often desired as noted above, it is a disaster experimentally, i. If it is unknown whether or not the behaviors under study are functionally independent, or if one of the goals of the research is to examine generalization for example across word sets, then a multiple baseline across participants can be combined with the multiple baseline across behaviors.
In this case, treatment is sequentially applied across participants following baselines phases of increasing length. The logic here is that treatment will affect behavior when and only when it is applied. Thus, if it is the treatment, and not extraneous variables, that are responsible for the behavioral effect, no change will be seen for any participant during baseline, regardless of its length.
This extra design component serves as an insurance policy; if generalization occurs, experimental control is maintained. The purpose of the experiment was to examine the effects of semantic complexity as determined by the typicality of items entered into treatment on naming in fluent aphasia.
Three sets of words were selected from two semantic categories. The word sets were comprised of either typical items within the category e. The hypothesis of the study was that training less semantically complex items i. Using a multiple baseline design across behaviors, one set of words was trained at a time while generalization was observed to the untrained sets.
When generalization did not occur, treatment was extended to the next set, and so on, until all sets were trained. For the second category vegetables treatment was first applied to atypical items and generalization to untrained items was noted. This same pattern was noted across participants.
Thus experimental control was accomplished when the order of treatment was typical—intermediate—atypical, but was lost when the order was switched to atypical—intermediate—typical. Since this was an expected outcome of the study, an additional design component was included, i. Therefore, even though generalization occurred with the latter treatment schedule, experimental control was demonstrated. Multiple baseline design used by Kiran and Thompson to investigate the effects of semantic complexity in treatment of naming in fluent aphasic participants.
Naming performance on typical, intermediate, and atypical items for the category birds and that on atypical, intermediate, and typical items for the category vegetables is shown for Participant 1 in the study. There are other types of single subject controlled experimental designs that can be used to examine the effects of treatment, however, the multiple baseline strategy is the most commonly used and is likely the best suited for most studies of aphasia.
One important point is that studying the differential effects of two or more treatments is difficult within a single subject experimental framework. While this can be done using an Alternating Treatments Design ATD , it is difficult to control for carry over effects from one treatment to another.
In such a design, each study participant simultaneously receives all treatments under investigation in an alternating manner, with the order of presentation of each treatment counterbalanced across treatment sessions and participants, e.
Following daily delivery of each treatment, the dependent measures are administered. For example, consider a studying examining the effects of two different approaches for improving word retrieval. Each day, both treatments are applied and word retrieval is measured following each. The problem is that, given that word retrieval improves, there is no way to know which treatment or whether both caused the improvement.
While there are ways to overcome this problem, for example, each treatment can be applied to functionally independent language behaviors e. The purpose of the study was to examine the differential effects of two lexically based treatment approaches to naming, a phonological cueing treatment PCT and a semantic cueing treatment SCT , in a patient with chronic anomia. Following baseline, the two treatments were simultaneously applied to two separate word sets sets 1 and 2 , while sets 3 and 4 remained in the baseline condition.
Once an acquisition effect was noted for the first two sets, the two treatments were simultaneously applied to the second two word sets. As can be seen experimental control was demonstrated, since improved naming was noted for all trained sets when treatment was given, but not during baseline testing.
What is unclear is which treatment resulted in the treatment effects. It is possible that both treatments were effective, with the semantic treatment showing a slightly stronger effect, as concluded by Wambaugh Or it is possible that only one of the treatments was effective and that generalization occurred from the effective treatment to the word set assigned to the other treatment.
While this is unlikely since there was no generalization effect of treatment from sets 1 and 2 to 3 and 4, it a potential explanation. The point here is that it is not possible to completely rule out carry over effects using an ATD. Thus, in general, group designs are better suited for examining the differential effects of treatment. Alternating treatment design, combined with a multiple baseline design across behaviors, used by Wambaugh to examine the effects of phonologic cueing PCT vs.
Percentage correct naming of word sets is shown across phases of the study. In this section, published reports of aphasia treatment in which single subject controlled designs were used are considered. The papers using single subject controlled designed were further analyzed for their technical merit and compared with findings derived from previous reviews of single subject research in aphasia treatment by Kearns and Thompson and Thompson and Kearns from to 2 , and by Thompson from to 3.
Several aspects of single subject controlled designs were evaluated, including a demonstration of experimental control or internal validity, b replication within and across participants, c operational specificity of independent and dependent measures, and d reliability of measurement.
As can be seen in Fig. Trends over the years show that in most all years there were greater numbers of single subject experiments than the other design types; a high number of case studies with no experimental control or internal validity were found; and fewer group studies were found as compared to the other design types. With respect to the frequency of single subject controlled and group experiments, these data are in keeping with the trends reported in the — review by Kearns and Thompson The situation regarding case studies, however, is surprising.
That case studies remain prevalent in the literature, however, suggests that both researchers and journal editorial boards remain unconvinced that powerful designs affording experimental control are required in aphasia treatment research. This is not to say that case studies do not have their place in the aphasia treatment literature. They are particularly worthy of publication if a novel approach to treatment is discussed, which can later be tested in a controlled study.
However, the case studies in the aphasia literature are largely not of this type. Notably, when examined by the journal in which aphasia treatment research has been published, the majority of papers appeared in Aphasiology , including 25 case studies, 32 single subject controlled studies, and 10 group studies. In review of the single subject controlled aphasia treatment studies, Fig. While the trend toward well-controlled experiments over the years is encouraging, these data indicate that the mere use of a single subject design does not constitute an experimentally controlled study.
One common problem is inherent in the use of A—B—A— B designs. As noted above, such designs require a return to baseline level performance in the second A phase; when this does not occur, the design is in essence an A—B with maintenance testing in the second A phase. In this case, the influence of extraneous variables on patient performance cannot be ruled out.
For example, change from the A to B phase could have resulted from spontaneous recovery of from a myriad of other variables that occurred at the same time that treatment was applied. Several researchers have encountered this problem e. Published single subject controlled experimental studies demonstrating internal validity in —, —, and — reviews of the literature. These reviews also found that not all studies include enough participants to establish replication within and across participants.
As noted above, single subject controlled experimentation does not mean that studying only a single subject is required. As noted above, such replication is essential for both internal and external validity purposes—replication within participants addresses internal validity, whereas replication across participants addresses external validity. As the number of replications across participants increases, confidence that the effects of the study can be generalized also increases.
Number of participants in published single subject controlled experiments in —, —, and — reviews of the literature. Operational definition of variables was evaluated in the — and — papers only. In these two series, the extent to which the dependent and independent variables were described such that they could be replicated either for research or clinical purposes indicated a general trend toward better definition of these variables.
Over the years an increase in the number of studies including reliability data on the dependent variable also was noted. While this upward trend is encouraging, these data show that not all single subject experimental researchers, even in the most recent review, are gathering reliability data as part of their experiments. Published single subject controlled experiments reporting reliability data in —, —, and — reviews of the literature.
The data concerning reliability on the independent variable are disappointing. As noted above, these data provide a measure of assurance that the treatment was applied as described. Indeed, adherence to experimental protocols in treatment research is essential such that the treatment effect can be attributed to its application as described by the researcher. This paper has emphasized the rationale behind single subject controlled experimentation, provided some critical distinctions between group and single subject approaches, detailed the technical requirements of single subject designs, and presented trends in the aphasia treatment literature, where single subject controlled designs have been utilized.
While single subject controlled experiments are often used in aphasia treatment research, there remain a larger number of case studies, which lack the experimental control that permits valid conclusions to be drawn about the functional relationship between independent and dependent variables. In addition, many published single subject controlled experiments have been unsuccessful in establishing experimental control, particularly those in which an A—B—A— B design is employed.
Further, some researchers continue to include only one participant in their studies and even when more than one participant is studied, the total number is inadequate for proper within and across subject replication. Finally, it was noted that while operational definitions of dependent and independent variables often are reported in published studies, not all studies include reliability data on the dependent measures, and very few include reliability on the independent variable.
Future research using single subject controlled designs could benefit from consideration of these requirements. In spite of the shortcomings found in some studies, numbers of well-designed experiments are available which attest to the applicability of single subject controlled designs to the study of aphasia treatment.
Using these designs, carefully selecting study participants for the specific nature of their language impairment, precisely describing the components of treatment as well as the outcome measures and carefully gathering reliability data, researchers have discovered treatments that are effective for patients with certain types of language impairments.
As pointed out by Holland et al. What we need to know now is what treatment s to provide for what disorder s. Progress toward answering this question has clearly been made. Many studies also have addressed the generalization of treatment effects and have shown that treatment often impacts both untrained language behaviors response generalization and language use in untrained conditions stimulus generalization.
Indeed, knowing the effects of specific types of treatment for patients with certain language impairments as well as understanding the extent to which these treatments result in generalized language use is important particularly in the current health care climate, which imposes limitations on the treatment that can be provided. This is not to say that our work is done, as further work detailing the effects of certain treatments for certain language deficits is needed.
Direct and systematic replication of established effects also is necessary in order to enhance the generalizability of findings.
In addition, there are many other unanswered questions regarding aphasia treatment effects. Among these are: When is treatment most effective? How often should treatment be provided? What treatment s work best for what language deficit s? The answers to these and other questions await further research, some of which can be elegantly addressed using single subject controlled experimental designs.
This is necessary for the data from the experiment to yield statistically relevant results. This requires the time and resources to not only gather the participants, but to run trials of the experiment on all the subjects to gather all the data.
An SSRD allows researchers to quickly design and run their study without having to find so many participants. While the fact that the researcher does not use a large number of participants has its advantages, it also has a downside: Because the experimental trials are run on only one subject, it is difficult to empirically show with the experiment's data that the findings will generalize out to larger populations.
All the trial can show is what happened with the individual subject, whereas traditional research designs that use large numbers of participants are specifically designed to show if a result is statistically valid for the general population. The purpose is to determine the effect of some experimental factor by introducing it to the experimental group, but not to the control group, and seeing what, if any, effect the experimental factor has.
However, in some cases researchers will use an alternative method called single-subject research design. Single Subject Research Designs SSRDs work by designing an experiment where, instead of a control group of subjects and an experimental group of subjects whose results are compared to one another, the control and experimental measurements come from a single subject. Researchers measure the metric of interest before introducing the experimental factor for a control measurement, and measure the metric of interest after introducing the experimental factor for the experimental measure.
While studies may include more than one subject, each subject is treated as a unique experiment instead of one trial in a larger experiment.
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