Introduction
The Patient-Specific Functional Scale (PSFS) is a highly regarded, patient-centered instrument designed to quantify activity limitation. First introduced in 1995 by P. Stratford, C. Gill, M. Westaway, and J. Binkley, the scale uniquely empowers patients to identify and rate functional activities they find difficult due to their condition. Consequently, this approach provides a personalized snapshot of functional ability, making it exceptionally valuable in physical therapy and rehabilitation contexts. Its profound impact on clinical practice and research is underscored by its accumulation of over 1,100 citations on Google Scholar.
This article, therefore, explores the PSFS’s features, applications, and psychometric properties, offering researchers and clinicians a comprehensive guide to leveraging this tool for enhanced patient-centered assessment.
Key Features of the Patient-Specific Functional Scale (PSFS)
Purpose and Use
The primary purpose of the PSFS is to assess and monitor the level of functional ability and daily activity limitations that the patient identifies. Because of its patient-driven nature, clinicians use it extensively to create tailored treatment plans and track progress over time. In addition, researchers frequently employ the PSFS as a key outcome measure in studies focused on rehabilitation, particularly for orthopedic conditions.
Target Population
Developers primarily validated the PSFS for adult populations, and it is suitable for a wide age range, including:
- Young Adults (18–24 years)
- Middle-Aged Adults (25–44 years)
- Older Adults (45–64 years)
- Seniors (65+ years)
Structure
Unlike traditional questionnaires with fixed items, the PSFS features a flexible and open format since the content does not restrict the user to a predefined set of items. Initially, clinicians ask the patient to identify up to three activities they have difficulty performing. Optionally, they can add two more activities, for a total of five. As a result, the domains it measures are unique to each individual and can include anything from walking and lifting to specific sports or household chores.
The questions are designed to be:
- Patient-specific: The patient selects activities based on their own priorities and daily life context.
- Quantitative: Each activity is rated using the 0–10 numeric scale. A score of ‘0’ indicates an inability to perform the activity, whereas a score of ’10’ signifies the ability to perform it at the same level as before the injury or condition.
In subsequent visits, clinicians re-evaluate the same activities identified in the initial assessment to measure progress. It is also permissible to add new activities that may have emerged during the follow-up period.
Scoring Method
The PSFS uses a straightforward rating system that is both quantitative and easy to interpret. The total score is calculated by summing the individual activity scores and dividing by the number of activities rated.
The scale is highly sensitive to change within an individual. For instance, the minimum detectable change (with 90% confidence) for an average score is 2 points, and for a single activity score, it is 3 points. If the score for Activity X improves from 3 to 7 this indicates positive change in function. This allows clinicians to confidently identify meaningful improvements.
Administration Format
Administering the PSFS is remarkably efficient, typically taking less than five minutes to complete. Furthermore, its flexible design allows for administration across all formats, including:
- Paper-based forms.
- Digital platforms.
- In-person or remote interviews.
- Mobile App.
- Phone/video call.
Although the scale is simple to use, it is designed to be administered by a clinician with basic clinical interviewing skills to help patients identify relevant activities
Applications of the Patient-Specific Functional Scale
The PSFS is a versatile tool with several key applications in both clinical practice and research settings.
- Monitoring: It is exceptionally useful for tracking a patient’s functional progress or decline across multiple sessions by reassessing the same self-identified activities.
- Treatment Planning: The scale provides clinicians with direct insight into a patient’s priorities, thereby helping to tailor rehabilitation programs to their specific functional goals.
- Research: Due to its high reliability and patient-centered focus, the PSFS serves as a robust outcome measure in clinical trials and studies evaluating the effectiveness of rehabilitation interventions.
Languages and Availability
To support its widespread use, the PSFS has been translated into over 25 languages, including:
- Arabic
- English
- Mandarin Chinese
- Spanish
- French
- German
- Japanese
The questionnaire is proprietary, so formal permission is required for its use. However, permission is often granted free of charge for academic or non-commercial clinical purposes.
Reliability and Validity
The PSFS is recognized as a highly reliable and valid instrument for functional assessment. Its psychometric soundness is supported by excellent statistical properties, including a test-retest reliability (ICC) of 0.97 and a standard error of measurement (SEM) of just 0.41 points on the 11- point scale. Numerous validation studies have confirmed its robustness across various patient populations, solidifying its status as a gold-standard measure in patient-specific functional assessment.
- The Original Validation Study link
- Measurement Properties in Patients with Knee Dysfunction link
- Measurement Properties of the Patient-Specific Functional Scale and its Current Uses study link
- Validation of the PSFS for Measuring Mobility-Related Goals in people with Multiple Sclerosis study link
- Reliability and Responsiveness in Patients Undergoing a Total Knee arthroplasty study link
- Validity and reliability of the Swedish version study link
- Validity of the PSFS in Community-Dwelling Older Adults study link
Limitations and Considerations
Despite its strengths, the PSFS has a few limitations:
- Narrow Focus: The scale is designed to measure functional activities only and does not capture other aspects of health, such as psychological well-being or pain intensity.
- Inter-Patient Comparability: Because the items are patient-generated, scores cannot be compared between different individuals. The tool is intended for tracking change within a single person.
Other Versions and Related Questionnaires
Currently, there are no official alternative versions of the PSFS. However, for a more comprehensive assessment, researchers and clinicians often use it alongside other region-specific or condition-specific tools, such as:
- Disabilities of the Arm, Shoulder and Hand (DASH).
- Oswestry Disability Index (ODI).
- Roland-Morris Disability Questionnaire (RMDQ).
- Lower Extremity Functional Scale (LEFS).
Additional Resources
- The Original Validation Study link.
- You can access the questionnaire as a PDF through this link.
- For inquiries, contact Dr. Stratford at stratfor@mcmaster.ca.
Frequently Asked Questions (FAQ)
- Who can use the PSFS?
Clinicians (such as physical therapists) and researchers use the PSFS for adults aged 18 and older to assess functional limitations in rehabilitation settings. - How long does it take to complete the PSFS?
The assessment is very quick, typically taking less than 5 minutes for patients and clinicians to complete. - How is the PSFS administered?
The questionnaire can be administered flexibly via paper-based forms, digital (online), mobile app, or through an in-person interview or through phone/video call. - Is there any cost to using the PSFS?
The PSFS is proprietary and requires permission for use. However, it is often available free of charge for non-commercial academic and clinical purposes.
A Word from ResRef about The Patient-Specific Functional Scale (PSFS)
The Patient-Specific Functional Scale (PSFS) is a widely used, patient- centered outcome measure that allows for personalized tracking of functional limitations in rehabilitation settings. Therefore, Its flexibility and simplicity make it a valuable tool, though users should be aware of its narrow scope focused on physical activity limitations.
References
- Stratford, P., Gill, C., Westaway, M., & Binkley, J. (1995). Assessing disability and change on individual patients: a report of a patient specific measure. Physiotherapy Canada, 47(4), 258-263. Link
- Chatman, A. B., Hyams, S. P., Neel, J. M., Binkley, J. M., Stratford, P. W., Schomberg, A., & Stabler, M. (1997). The Patient-Specific Functional Scale: measurement properties in patients with knee dysfunction. Physical therapy, 77(8), 820-829.‏ Link
- Pathak, A., Wilson, R., Sharma, S., Pryymachenko, Y., Ribeiro, D. C., Chua, J., & Abbott, J. H. (2022). Measurement properties of the patient-specific functional scale and its current uses: an updated systematic review of 57 studies using COSMIN guidelines. journal of orthopaedic & sports physical therapy, 52(5), 262-275. Link
- Mañago, M. M., Cohen, E. T., Cameron, M. H., Christiansen, C. L., & Bade, M. (2023). Reliability, validity, and responsiveness of the patient-specific functional scale for measuring mobility-related goals in people with multiple sclerosis. Journal of Neurologic Physical Therapy, 47(3), 139-145. Link
- Berghmans, D. D., Lenssen, A. F., van Rhijn, L. W., & de Bie, R. A. (2015). The patient-specific functional scale: its reliability and responsiveness in patients undergoing a total knee arthroplasty. journal of orthopaedic & sports physical therapy, 45(7), 550-556. Link
- Rosengren, J., & Brodin, N. (2013). Validity and reliability of the Swedish version of the Patient Specific Functional Scale in patients treated surgically for carpometacarpal joint osteoarthritis. Journal of Hand Therapy, 26(1), 53-61. Link
- Mathis, R. A., Taylor, J. D., Odom, B. H., & Lairamore, C. (2019). Reliability and validity of the patient-specific functional scale in community-dwelling older adults. Journal of Geriatric Physical Therapy, 42(3), E67-E72. Link
