MOS Physical Functioning Measure

Abstract

The MOS Physical Functioning Measure (PFM) is a specialized scale developed as part of the Medical Outcomes Study (MOS). It is designed to evaluate an individual’s capacity to perform a variety of physical activities and assess limitations imposed by their health status. The scale is widely recognized for its contribution to measuring Physical Functioning, particularly within chronic disease populations. The PFM is often cited as the foundational component for the physical functioning domain in broader health surveys, such as the SF-36, providing a robust, multi-item assessment of functional mobility and self-care activities.

Keywords

Physical functioning, Medical Outcomes Study, MOS, health status, quality of life, functional limitations, self-report scale, psychometrics, activities of daily living.

Authors

Anita L. Stewart, Cathy J. Kamberg, Ron D. Hays, John E. Ware, Jr.

Purpose

The primary purpose of the MOS Physical Functioning Measure is to quantify the extent to which an individual’s health limits their ability to engage in common physical tasks. This measure moves beyond simple dichotomous assessments by employing a graded response scale to capture the severity of limitations, ranging from vigorous activities to basic self-care. It serves as a vital tool for clinicians and researchers monitoring changes in Health Status over time, evaluating treatment efficacy, and assessing the overall impact of illness on daily life.

The scale was developed to provide a standardized, reliable component for the comprehensive assessment of patient outcomes within the broader framework of the Medical Outcomes Study. By focusing specifically on physical capacity, the PFM allows for detailed analysis of mobility and functional independence, critical indicators of overall Quality of Life (QoL).

Construct

The core construct measured by the MOS Physical Functioning Measure is Physical Functioning, defined as the degree to which health limits routine physical activities. This construct encompasses both gross motor activities (like walking and climbing stairs) and strenuous activities (like running or participating in sports), as well as essential self-care tasks (like bathing or dressing). The scale operationalizes physical functioning by requiring respondents to rate their degree of limitation across these various domains.

The scale effectively captures a hierarchy of physical difficulty, from highly demanding activities (vigorous exercise) to basic activities of daily living (ADLs). The additional items in the measure assess related concepts, such as satisfaction with physical ability, dependency on assistance, and confinement due to health, providing a broader context for the measured physical limitations.

Validity

The validity of the MOS Physical Functioning Measure has been extensively documented, largely due to its inclusion in the foundational work leading to the SF-36. Construct validity is supported by its strong correlation with other established measures of physical health and its ability to differentiate between groups with known differences in health status, such as patients with chronic conditions versus healthy populations. The hierarchical nature of the items (from mild to severe limitation) also provides evidence of good face and content validity.

Studies conducted during the Medical Outcomes Study confirmed that the PFM component demonstrated expected relationships with other dimensions of health, including role limitations due to physical problems and general health perceptions. This robust validation process ensures that the scale accurately captures the intended construct of functional limitations.

Reliability

The PFM exhibits strong Reliability, a characteristic essential for high-quality Psychometric Properties. Internal consistency, typically measured using Cronbach’s alpha, has consistently been reported as high (often exceeding 0.90) across diverse patient populations. This indicates that the items within the scale measure a unified underlying construct (physical functioning).

Test-retest reliability is also generally high, suggesting that the scale provides stable measurements of physical function over short periods, assuming the patient’s underlying health status has not changed significantly. This stability makes the PFM highly suitable for longitudinal studies tracking patient recovery or disease progression.

Factor Analysis

Factor analytic studies, particularly those related to the development of the SF-36, consistently confirm that the physical functioning items load strongly onto a single, dominant factor. This supports the conceptualization of Physical Functioning as a unitary domain within the broader health profile measured by the MOS instruments. While the original scale includes additional items (satisfaction, assistance, etc.), the ten core activity limitation items (PF-10) are highly cohesive.

Research suggests that the PFM forms one of the two primary summary components—the Physical Component Summary (PCS)—when combined with other MOS scales like Role Physical and Bodily Pain. The clear factor structure contributes significantly to the scale’s utility in clinical and population health research.

Instrument

Test Type: Self-administered health status questionnaire/Psychometric scale.

Format: 14 items total (10 core activity items, 4 supplementary items). Response formats vary, utilizing 3-point and 6-point Likert scales, and categorical yes/no responses for dependency and confinement.

Language Available: Primarily English; widely translated into numerous languages due to its integration into the SF-36 instrument suite.

Population Group: General population, chronic disease patients, and clinical populations requiring assessment of functional limitations.

Age Group: Adults (typically 18 years and older).

Population Details: Originally validated in heterogeneous patient populations participating in the Medical Outcomes Study, including those with chronic conditions such as hypertension, diabetes, depression, and heart disease.

Test Methodology: Respondents are asked to report the degree to which their current health limits them in performing specific physical activities.

Keywords

Physical health, functional mobility, ADLs, Medical Outcomes Study, health outcomes, scale development, fitness measurement, self-report.

Authors

Author ORCID Identifier: Information not provided in source material.

Affiliation Email addresses: Information not provided in source material.

Correspondence Address: Information not provided in source material.

Permissions & Fee and Test Year

The scale was developed as part of the Medical Outcomes Study, with key publications detailing the physical functioning measures appearing in 1992. Permission requirements for use often depend on the specific version (e.g., the original MOS version vs. the SF-36 component). Academic and non-commercial use may be granted freely, but commercial use or modified versions may require licensing from the scale administrators (e.g., RAND Corporation or QualityMetric).

Test Year: 1992 (Key publication by Stewart & Kamberg).

Reference’s

The scale and its development are detailed in several seminal works related to the MOS approach:

• Stewart, Anita L., Hays, Ron D. and Ware, John E., (1988). The MOS Short-Form General Health Survey: Reliability and Validity in a Patient Population. Medical Care, 26(7): 724-735.
• Stewart, AL., Kamberg, CJ. (1992). Physical functioning measures. In: Stewart, AL., Ware, JE., Jr., eds. Measuring functioning and well-being: the Medical Outcomes Study approach. Durham, North Carolina: Duke University Press, 86–101.
• Sherbourne, CD., Stewart, AL., Wells, KB. (1992). Role functioning measures. In: Stewart, AL., Ware JE, Jr., eds. Measuring functioning and well-being: the Medical Outcomes Study approach. Durham, North Carolina: Duke University Press, 1992:205–219.
• Raina, P., Bonnett, B., Waltner-Toews, D., et al. (1999). How reliable are selected scales from population-based health surveys? An analysis among seniors. Can J Public Health, 90:60–64.
• McDowell, Ian. (2006). Measuring Health: A Guide to Rating Scales and Questionnaires, Third Edition. OXFORD UNIVERSITY PRESS.

The original PDF detailing the instrument can be downloaded here: www.a4ebm.org/sites/default/files/Measuring%20Health.pdf

Further documentation regarding the MOS methodology is available here: https://www.rand.org/content/dam/rand/pubs/monograph_reports/2008/MR162.pdf

Items of the MOS Physical Functioning Measure

IMPORTANT: The following scale items must be preserved in their original language and must not be changed in any way.

ACTIVITIES

1- Yes, limited a lot; 2-Yes, limited a little; 3-No, not limited at all

• Vigorous activities, such as running, lifting heavy objects, participating in strenuous sports.
• Moderate activities, such as moving a table, pushing a vacuum cleaner, bowling, or playing golf.
• Lifting or carrying groceries
• Climbing several flights of stairs
• Climbing one flight of stairs
• Bending, kneeling or stooping
• Walking more than one mile
• Walking several blocks
• Walking one block
• Bathing or dressing yourself

2. How satisfied are you with your physical ability to do what you want to do? (Circle One)

Completely satisfied . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Very satisfied . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Somewhat satisfied. . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Somewhat dissatisfied . . . . . . . . . . . . . . . . . . . . . . . . 4

Very dissatisfied . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Completely dissatisfied. . . . . . . . . . . . . . . . . . . . . . . . 6

3. When you travel around your community, does someone have to assist you because of your health? (Circle One)

Yes, all of the time . . . . . . . . . . . . . . . . . . . . . . . . . 1

Yes, most of the time . . . . . . . . . . . . . . . . . . . . . . . . 2

Yes, some of the time . . . . . . . . . . . . . . . . . . . . . . . 3

Yes, a little of the time . . . . . . . . . . . . . . . . . . . . . . . 4

No, none of the time . . . . . . . . . . . . . . . . . . . . . . . . 5

4. Are you in bed or in a chair most or all of the day because of your health? (Circle One)

Yes, every day . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Yes, most days . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Yes, some days . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Yes, occasionally . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

No, never . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

5. Are you able to use public transportation?

(Circle One)

No, because of my health . . . . . . . . . . . . . . . . . . . . . 1

No, for some other reason . . . . . . . . . . . . . . . . . . . . 2

Yes, able to use public transportation . . . . . . . . . . . . 3