RAND Medical Outcomes Study – 20 items

Abstract

The RAND Medical Outcomes Study (MOS) 20-item measure is a highly influential, patient-administered questionnaire developed as part of the larger Medical Outcomes Study (MOS) initiative. This instrument serves as an early, abbreviated tool for assessing key aspects of a patient’s Health-Related Quality of Life (HRQoL), typically reflecting experiences over the preceding four weeks. Although its successors, the SF-36 and SF-12, became more widely utilized, the 20-item structure captures essential domains including physical functioning, bodily pain, social activities, and mental health. The scale is frequently scored to yield two major summary measures: the Physical Health Composite (PCS) and the Mental Health Composite (MCS), which are vital for longitudinal monitoring and comparative effectiveness research.

Keywords

Health-Related Quality of Life, HRQoL, Medical Outcomes Study, MOS, RAND, Patient-Reported Outcomes, PROs, Physical Functioning, Mental Health, SF-20.

Authors

John E. Ware, Jr., Allyson L. Stewart, Ron D. Hays, M. Kosinski, S.D. Keller.

Purpose

The primary purpose of the RAND MOS 20-item scale is to provide a concise, standardized, and psychometrically sound measure of general health status and functional limitations. It was specifically designed during the original MOS project to be sensitive enough to detect clinically meaningful changes in health status over time, thereby allowing researchers and clinicians to track patient progress.

The instrument is widely used in clinical research, population health surveillance, and health policy analysis. It facilitates the evaluation of outcomes across diverse patient groups, enabling comparisons of the impact of various diseases and treatments on patients’ daily lives and overall well-being. Its efficiency makes it suitable for large-scale epidemiological studies where respondent burden must be minimized.

Construct

The scale measures the multi-dimensional construct of Health-Related Quality of Life (HRQoL). HRQoL is defined as the subjective perception of the impact of health status, including disease, injury, and treatment, on a person’s physical, psychological, and social functioning.

The 20-item version measures six primary domains, which are integrated into the two summary scores (PCS and MCS). These domains include Physical Functioning (limitations in physical activities), Role Limitations due to physical health, Bodily Pain, General Health Perceptions, Social Functioning, and specific aspects of Mental Health (such as anxiety, depression, and psychological well-being).

Validity

The validity of the RAND MOS 20-item instrument is firmly established within the rigorous psychometric framework of the MOS family of measures. Content validity is ensured as the items were derived from the extensive original MOS battery, meticulously covering critical dimensions of patient functioning and well-being identified through expert consensus and patient input.

Construct validity has been repeatedly demonstrated through studies confirming the hypothesized relationships among the subscales and the successful differentiation between the physical and mental health composite scores. The scale also exhibits robust criterion validity, showing expected correlations with external measures of disease severity, clinical diagnoses, and utilization of healthcare services, indicating that it accurately measures what it intends to measure.

Reliability

The reliability of the 20-item scale is generally considered high, consistent with the high standards set by the related SF measures. Internal consistency, assessed by measures such as Cronbach’s alpha, typically meets or exceeds the threshold of 0.80 for most primary domain scales, particularly for the Physical Functioning and Mental Health domains, indicating strong homogeneity among items within each respective domain.

Furthermore, studies examining test-retest reliability confirm the stability of the scores over short measurement intervals in populations whose health status is stable. This stability ensures that the instrument provides dependable measurements, minimizing random error and maximizing confidence that observed score changes are attributable to genuine changes in the patient’s underlying health status.

Factor Analysis

Factor analysis of the MOS instruments, including the components utilized in the 20-item version, consistently supports a clean, two-factor orthogonal structure. This structure is crucial for deriving the two principal summary scores: the Physical Health Composite (PCS) and the Mental Health Composite (MCS).

The Physical Health Composite (PCS) factor is defined by high loadings from items assessing physical activities, physical role limitations, and bodily pain. The Mental Health Composite (MCS) factor receives high loadings from items related to emotional state, psychological distress (nervousness, feeling downhearted), and general mental well-being. This clear factorial separation confirms that the scale effectively captures two distinct, yet interacting, dimensions of global health.

Instrument

Test Type: Patient-Reported Outcome (PRO) measure; Health Status Questionnaire

Format: Self-administered questionnaire utilizing categorical and Likert-type response options.

Language Available: English (Original); numerous translations exist for the broader MOS/SF framework.

Population Group: General population; individuals with chronic illnesses; clinical trial participants.

Age Group: Typically 14 years and older (used primarily with adults).

Population Details: Originally developed and validated on a large cohort of patients participating in the Medical Outcomes Study in the United States, including those with common chronic conditions.

Test Methodology: Raw scores are typically aggregated and transformed using standardized algorithms into norm-based T-scores for the PCS and MCS, scaled such that the mean of the reference population is 50 with a standard deviation of 10.

Keywords

Health status, Patient quality of life, PCS, MCS, Short-Form Survey, Psychometrics, Outcome measurement, Functioning, Reliability, Validity.

Authors

Author ORCID Identifier: N/A (Historically developed)

Affiliation Email addresses: N/A (Contact RAND Corporation for official inquiries regarding the instrument)

Correspondence Address: RAND Corporation, Health Program, Santa Monica, CA, USA.

Permissions & Fee and Test Year

The conceptualization and initial development of the core components of this measure occurred during the Medical Outcomes Study (MOS) project, which began in the mid-1980s. The resulting instruments, including the 20-item version, are foundational to subsequent measures like the SF-36.

Permissions and Fees: The RAND Corporation holds the intellectual property rights to the MOS instruments. While many MOS measures are available for non-commercial research and educational use, researchers must confirm specific licensing requirements. For commercial use or use of derivative works (like the SF-12/36 Version 2), licensing is typically managed by QualityMetric Incorporated. Information regarding the related 36-item Short Form can be found at: http://www.rand.org/health/surveys_tools/mos/36-item-short-form.html

Reference’s

1. Stewart, A.L., Hays, R.D., Ware, J.E, Jr. (1992). Health perceptions, energy/fatigue, and health distress measures. In: Stewart AL, Ware JE, Jr., eds. Measuring functioning and wellbeing: the Medical Outcomes Study approach. Durham, NC: Duke University Press, 143–172.

2. Ware, J.E, Jr., Kosinski, M., Keller, S.D. (1995). How to score the SF-12 physical and mental health summary scales. Boston: The Health Institute, New England Medical Center.

3. Ware, J.E, Jr., Kosinski, M., Keller, SD. (1996). A 12- Item Short-Form Health Survey: construction of scales and preliminary tests of reliability and validity. Med Care, 34:220–233.

4. Ware, J.E, Jr., Kosinski, M., Turner-Bowker, D.M., et al. (2002). How to score Version 2 of the SF-12 et al. Health Survey. Lincoln, Rhode Island: QualityMetric Inc.

5. Bennett, S.J., Oldridge, N.B., Eckert, G.J., et al. (2002). Discriminant properties of commonly used quality of life measures in heart failure. Qual Life Res, 11:349–359.

6. McDowell, Ian. (2006). Measuring Health: A Guide to Rating Scales and Questionnaires, Third Edition. OXFORD UNIVERSITY PRESS

Items of the RAND Medical Outcomes Study -20 items

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

Patient Questionnaire

Choose one option for each questionnaire item.

1. In general‚ would you say your health is:

   • 1)   Excellent
   • 2)   Very good
   • 3)   Good
   • 4)   Fair
   • 5)   Poor

2. For how long (if at all) has your health limited you in each of the following activities?

   • a.    The kinds or amounts of vigorous activities you can do‚ like lifting heavy objects‚ running or participating in strenuous sports
     Limited for more than 3 months (1); Limited for 3 months or less (2); Not limited at all (3)
   • b.    The kinds or amounts of moderate activities you can do‚ like moving a table‚ carrying groceries‚ or bowling
     Limited for more than 3 months (1); Limited for 3 months or less (2); Not limited at all (3)
   • c.    Walking uphill or climbing a few flights of stairs
     Limited for more than 3 months (1); Limited for 3 months or less (2); Not limited at all (3)
   • d.    Bending‚ lifting‚ or stooping
     Limited for more than 3 months (1); Limited for 3 months or less (2); Not limited at all (3)
   • e.    Walking one block
     Limited for more than 3 months (1); Limited for 3 months or less (2); Not limited at all (3)
   • f.     Eating‚ dressing‚ bathing‚ or using the toilet
     Limited for more than 3 months (1); Limited for 3 months or less (2); Not limited at all (3)

3. How much bodily pain have you had during the past 4 weeks:

   • 1)   None
   • 2)   Very mild
   • 3)   Mild
   • 4)   Moderate
   • 5)   Severe
   • 6)   Very Severe

4. Does your health keep you from working at a job‚ doing work around the house‚ or going to school?

   • 1)   YES‚ for more than 3 months
   • 2)   YES‚ for 3 months or less
   • 3)   NO

5. Have you been unable to do certain kinds or amounts of work‚ housework‚ or schoolwork because of your health?

   • 1)   YES‚ for more than 3 months
   • 2)   YES‚ for 3 months or less
   • 3)   NO

For each of the following questions‚ please mark the circle for the one answer that comes closest to the way you have been feeling during the past month.

6. How much of the time‚ during the past month‚ has you health limited your social activities (like visiting with friends or close relatives)? All of the time (1); Most of the time (2); A good bit of the time (3); Some of the time (4); A little of the time (5); None of the time (6)

7. How much of the time‚ during the past month‚ have you been a very nervous person? All of the time (1); Most of the time (2); A good bit of the time (3); Some of the time (4); A little of the time (5); None of the time (6)

8. During the past month‚ how much of the time have you felt calm and peaceful? All of the time (1); Most of the time (2); A good bit of the time (3); Some of the time (4); A little of the time (5); None of the time (6)

9. How much of the time‚ during the past month‚ have you felt downhearted and blue? All of the time (1); Most of the time (2); A good bit of the time (3); Some of the time (4); A little of the time (5); None of the time (6)

10. During the past month‚ how much of the time have you been a happy person? All of the time (1); Most of the time (2); A good bit of the time (3); Some of the time (4); A little of the time (5); None of the time (6)

11. How often‚ during the past month‚ have you felt so down in the dumps that nothing could cheer you up? All of the time (1); Most of the time (2); A good bit of the time (3); Some of the time (4); A little of the time (5); None of the time (6)

12. Please mark the circle that best describes whether each of the following statements is true or false for you.

    • a.    I am somewhat ill
      Definitely true (1); Mostly true (2); Not sure (3); Mostly false (4); Definitely false
    • b.    I am as healthy as anybody I know
      Definitely true (1); Mostly true (2); Not sure (3); Mostly false (4); Definitely false
    • c.    My health is excellent
      Definitely true (1); Mostly true (2); Not sure (3); Mostly false (4); Definitely false
    • d.    I have been feeling bad lately
      Definitely true (1); Mostly true (2); Not sure (3); Mostly false (4); Definitely false

Physical Health Composite (PCS) and Mental Health Composite (MCS)