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  1. What characteristic(s) of single-subject studies are different from a randomized clinical trial?

  2. What are the primary differences between qualitative and quantitative research designs?

  3. What types of clinical questions are best addressed with a qualitative research study?


This chapter will help you understand the following:

  1. Advantages and disadvantages of single-subject research designs

  2. The appraisal of the applicability, quality, and results of single-subject research designs

  3. Characteristics of qualitative research studies

  4. The appraisal of the applicability, quality, and results of qualitative research


Single-subject and qualitative research are discussed in this chapter. These two types of research are not common in the physical therapy literature, but both types are useful for supporting clinical decision-making. 1 Many of the appraisal concepts described in previous chapters can be applied to single-subject research; therefore, they are mentioned but not repeated in-depth in this chapter. The different concepts used in the appraisal of qualitative research are addressed in more detail.


Understanding single-subject experimental designs, analyses, and applications improves your ability to evaluate the evidence based literature and, eventually, to answer your clinical questions. Rigorous research with single participants can sometimes be applied more directly to your patients than the results from a group of participants in a randomized clinical trial (RCT). In a typical single-subject design (SSD), one participant is followed intensely. Before intervention begins, the variables of interest (outcome measures) are repeatedly measured during a baseline period. This period may occur over successive days or weeks, and it establishes what is typical for each outcome measure for the participant. For example, the gait characteristics of a participant walking on a treadmill might be measured every day for a week.

The intervention period begins after baseline, during which data are collected periodically on the participant. There might be an additional period after intervention when the participant is measured, but no treatment is given. The change in the variables during the treatment period is then compared to the variables during baseline and post-treatment periods. An SSD typically creates abundant data from one participant.

An SSD study may use many participants, each treated and analyzed separately. For example, Laessker-Alkema and Eek2 studied 10 children with cerebral palsy and the use of orthoses to improve their motor function. The children studied spanned 5 to 14 years of age. Each participant was studied in-depth, and conclusions were made on a case-by-case basis. The positive results were summarized across all subjects, but individual data were presented.

Case studies differ from an SSD because they are typically written retrospectively, and they detail the characteristics of one case and the course of intervention for that case. A case study is not a controlled single-subject experimental design, and the two terms should not be interchanged. A case study is a systematically reported single-patient example that does ...

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