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  1. How does the appraisal process change when considering prognostic research in comparison to intervention research?

  2. What typical study designs for prognostic research are you likely to find in the literature?

  3. What is the flaw in the following statement about a regression analysis?

    It appears that subject weight, previous injuries, and type of profession were all causes of low back pain.


This chapter will help you understand the following:

  • Application of prognostic literature to specific patients and patient groups

  • Appraisal of the validity of prognostic studies

  • Interpretation of the results of prognostic studies


Patients, families, and physical therapists have many questions about prognosis. Prognostic questions may be about the impact of a disease or event on a patient’s long-term outcome. For example, a patient may ask, “Will I be able to ski after back surgery?” or “When can I expect to go back to work?” Prognostic questions may also guide discharge planning. You may ask, “What is the prognosis for my patient to return home versus a rehabilitation facility at discharge?” or “What are the odds that this intervention will benefit my patient’s independent ambulation?” Many factors influence the answers to prognostic questions, such as the severity of the patient’s problem, gender, age, home environment, and comorbidities.

Valid prognostic studies can assist in answering these types of questions, and they help weigh the various factors that may contribute to specific outcomes. The prognostic literature has specific types of designs and statistical analyses.

As discussed in previous chapters, appraisal is the third step in the five-step evidence based practice (EBP) process. In this chapter, you will develop your skills at appraising the literature on prognosis, completing all four parts of appraising prognostic literature:

  • Part A: Determining the applicability of a prognostic study

  • Part B: Determining the quality of a prognostic study

  • Part C: Interpreting the results of a prognostic study

  • Part D: Summarizing the clinical bottom line of a prognostic study


This chapter begins with descriptions of common designs for prognostic studies because these differ from the types of designs used for intervention studies. The same principles for searching the literature described in Chapter 2 also apply to searching the prognostic literature. However, the research designs most typically applied to prognostic questions are observational studies that explore associations between or among variables. These typically include cohort and case control designs (Fig. 6.1), which can be either longitudinal (participants are followed over time) or cross-sectional (participant data are collected at one point in time).


Examples of cohort, cross-sectional, and case control study designs.

Cohort Studies

In a cohort study, a group of participants who are likely ...

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