Patient Specific Functional Scale
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The Patient-Specific Functional Scale (PSFS) is a self-reported, patient-specific measure, designed to assess functional change, primarily in patients presenting with musculoskeletal disorders The scale was developed by Stratford and colleagues 70 as a self-report measure of function that could be used in patients with varying levels of independence. It was designed to provide clinicians with a valid, reliable, responsive, and efficient outcome measure that would be easy to use and applicable to a large number of clinical presentations.
As a clinical outcome measure, the PSFS allows patients to report on their functional status at baseline and at a follow-up session, to determine if a meaningful change in functional status has occurred.
Population Tested 
- Joint Replacement
- Knee Dysfunction
- Low back pain
- Lower Limb Amputees
- Multiple Sclerosis
- Neck Dysfunction and Whiplash
- Pubic Symphysis pain in pregnancy
- Spinal Stenosis
- Upper Extremity Musculoskeletal Conditions
Patients are asked to identify up to five important activities they are unable to perform or are having difficulty with as a result of their problem. In addition to identifying the activities, patients are asked to rate, on an 11-point scale, the current level of difficulty associated with each activity.Following the intervention, patients are again asked to rate the activities previously identified and are given the chance to nominate new problematic activities that might have arisen during that time. In the 11 point scale
- "0" represents “unable to perform”
- "10" represents “able to perform at prior level”
Patients select a value that best describes their current level of ability on each activity assessed.
The PSFS is a valid, reliable, and responsive outcome measure for patients with back, neck, knee and upper extremity problems.
The reliability of any outcome measure is assessed by the consistent scores it produces on multiple testing, with high test-retest reliability indicating that, when repeated under the same conditions, the measure is likely to yield the same results. For PSFS various authors have calculated the test-retest reliability using Intraclass correlation coefficient (ICC), which gives a score between 0 and 1 for the outcome measure being assessed. The closer the score is to 1, the more reliable the outcome measure. 
The validity of an outcome measure indicates that the measurement instrument is evaluating what it proposes to evaluate.For an outcome measure to be accepted and utilized within a clinical setting, it should be assessed for its proposed purpose and shown to be applicable in a specified population.
Responsiveness of an outcome measure is the ability of outcome measure to assess changes over time. Responsiveness, or sensitivity to change, can be measured and defined in terms of internal and external responsiveness and evaluated using a number of different approaches. 
- Horn KK, Jennings S, Richardson G, Van Vliet D, Hefford C, Abbott JH. The patient-specific functional scale: psychometrics, clinimetrics, and application as a clinical outcome measure. journal of orthopaedic & sports physical therapy. 2012 Jan;42(1):30-D17.
- Stratford P, Gill C, Westaway M, Binkley J. Assessing disability and change on individual patients: a report of a patient specific measure. Physiother Can. 1995;47:258-263. http://dx.doi. org/10.3138/ptc.47.4.258
- Hefford C, Abbott JH, Arnold R, Baxter GD. The patient-specific functional scale: validity, reliability, and responsiveness in patients with upper extremity musculoskeletal problems. journal of orthopaedic & sports physical therapy. 2012 Feb;42(2):56-65.
- Stratford P, Gill C, Westaway M, Binkley J. Assessing disability and change on individual patients: a report of a patient specific measure. Physiotherapy canada. 1995 Oct;47(4):258-63.
- Beattie P. Measurement of health outcomes in the clinical setting: applications to physiotherapy. Physiotherapy theory and Practice. 2001 Jan 1;17(3):173-85.