Stephen M. Haley

Evaluation of the MOS SF-36 physical functioning scale (PF-10) : I. Unidimensionality and reproducibility of the Rasch item scale

Indexes developed to measure physical functioning as an essential component of general health status are often based on sets of hierarchically-structured items intended to represent a broad underlying concept. Rasch Item Response Theory (IRT) provides a methodology to examine the hierarchical structure, unidimensionality, and reproducibility of item positions (calibrations) along a scale. Data gathered on the 10-item Physical Functioning Scale (PF-10) from a large sample of Medical Outcomes Study patients (N = 3445) were used to examine the hierarchical order, unidimensionality, and reproducibility of item calibrations. Rasch-IRT analyses generated an empirical item hierarchy, confirmed the unidimensionality of the PF-10 for most patients, and established the reproducibility of item calibrations across patient populations and repeated tests. These findings support the content validity of the PF-10 as a measure of physical functioning and suggest that valid Rasch-IRT summary scores could be generated as an alternative to the current Likert summative scores. Unidimensionality and reproducibility of the item scale are essential prerequisites for the development of Rasch-based person measures of physical functioning that can be used across populations and over repeated tests.

Are the ICF Activity and Participation dimensions distinct

OBJECTIVE To test the hypothesis that distinct Activity and Participation dimensions of the International Classification of Functioning, Disability, and Health could be identified using physical functioning items drawn from the Late Life Function and Disability Instrument. DESIGN A cross-sectional, survey design was employed. SUBJECTS The sample comprised 150 community-dwelling adults aged 60 years and older. METHODS Exploratory factor analysis was used to identify interpretable dimensions underlying 48 physical functioning questionnaire items. RESULTS Findings revealed that one conceptual dimension underlying these physical functioning items was not sufficient to adequately explain the data (X2 = 2383; p < 0.0001). A subsequent solution produced 3 distinct, interpretable factors that accounted for 61.1% of the variance; they were labeled: Mobility Activities (24.4%), Daily Activities (24.3%), and Social/Participation (12.4%). All 3 factors achieved high internal consistency with coefficient alphas of 0.90 or above. CONCLUSION Within physical functioning, distinct concepts were identified that conformed to the dimensions of Activity and Participation as proposed in the ICF. We believe this is the first empirical evidence of separate Activity and Participation dimensions within the International Classification of Functioning, Disability, and Health classification.

Evaluation of the MOS SF-36 Physical Functioning Scale (PF-10): II. Comparison of relative precision using Likert and Rasch scoring methods.

This study examined the relative precision (RP) of two methods of scoring the 10-item Physical Functioning Scale (PF-10) from a large sample of patients (n = 3445) of the Medical Outcomes Study. Based on a Likert scaling model, the PF-10 summated scoring method was compared with a Rasch Item Response Theory (IRT) scaling model in which raw scores were transformed into a latent trait variable of physical functioning. Potential differences between scoring methods were hypothesized to be attributed to: (1) the logarithmic nature of the Rasch transformation; (2) the unevenness of the PF-10 item distributions; and (3) reduction of within-group variance. RP ratios favored the Rasch model in discriminating between patients who differed in disease severity. The Rasch and Likert scoring models performed similarly for tests involving sensitivity to change over a two-year follow-up period. In all comparisons, differences between methods were most apparent in clinical groups whose scores most approximated the extremes of the score distribution. Further research is necessary to test for differences between scoring models in discrimination and sensitivity to change among clinical groups whose scores are sufficiently spread across the continuum of physical functioning, in particular patients with either very high or low physical functioning. The Rasch model of scoring may have important implications for the clinical interpretation of individual scores at all ranges of the scale.

Validation of the late-life function and disability instrument

Objectives: To assess the concurrent and predictive validity of the Late‐Life Function and Disability Instrument (LLFDI).

Activity outcome measurement for postacute care.

BackgroundEfforts to evaluate the effectiveness of a broad range of postacute care services have been hindered by the lack of conceptually sound and comprehensive measures of outcomes. It is critical to determine a common underlying structure before employing current methods of item equating across outcome instruments for future item banking and computer-adaptive testing applications. ObjectiveTo investigate the factor structure, reliability, and scale properties of items underlying the Activity domains of the International Classification of Functioning, Disability and Health (ICF) for use in postacute care outcome measurement. MethodsWe developed a 41-item Activity Measure for Postacute Care (AM-PAC) that assessed an individual’s execution of discrete daily tasks in his or her own environment across major content domains as defined by the ICF. We evaluated the reliability and discriminant validity of the prototype AM-PAC in 477 individuals in active rehabilitation programs across 4 rehabilitation settings using factor analyses, tests of item scaling, internal consistency reliability analyses, Rasch item response theory modeling, residual component analysis, and modified parallel analysis. ResultsResults from an initial exploratory factor analysis produced 3 distinct, interpretable factors that accounted for 72% of the variance:Applied Cognition (44%), Personal Care & Instrumental Activities (19%), and Physical & Movement Activities (9%); these 3 activity factors were verified by a confirmatory factor analysis. Scaling assumptions were met for each factor in the total sample and across diagnostic groups. Internal consistency reliability was high for the total sample (Cronbach &agr; = 0.92 to 0.94), and for specific diagnostic groups (Cronbach &agr; = 0.90 to 0.95). Rasch scaling, residual factor, differential item functioning, and modified parallel analyses supported the unidimensionality and goodness of fit of each unique activity domain. ConclusionsThis 3-factor model of the AM-PAC can form the conceptual basis for common-item equating and computer-adaptive applications, leading to a comprehensive system of outcome instruments for postacute care settings.

Contemporary measurement techniques for rehabilitation outcomes assessment.

In this article, we review the limitations of traditional rehabilitation functional outcome instruments currently in use within the rehabilitation field to assess Activity and Participation domains as defined by the International Classification of Function, Disability, and Health. These include a narrow scope of functional outcomes, data incompatibility across instruments, and the precision vs feasibility dilemma. Following this, we illustrate how contemporary measurement techniques, such as item response theory methods combined with computer adaptive testing methodology, can be applied in rehabilitation to design functional outcome instruments that are comprehensive in scope, accurate, allow for compatibility across instruments, and are sensitive to clinically important change without sacrificing their feasibility. Finally, we present some of the pressing challenges that need to be overcome to provide effective dissemination and training assistance to ensure that current and future generations of rehabilitation professionals are familiar with and skilled in the application of contemporary outcomes measurement.

Comparison of Rasch and summated rating scales constructed from SF-36 physical functioning items in seven countries: results from the IQOLA Project. International Quality of Life Assessment

Rasch models for polytomous items were used to assess the scaling assumptions and compare item response patterns in the 10-item SF-36 physical functioning scale (PF-10) for general population respondents in Denmark, Germany, Italy, the Netherlands, Sweden, the United Kingdom, and the United States. The Rasch model of physical functioning developed in the United States was compared to models for other countries, and each country was compared to a multinational composite. Strong scale congruence across the seven countries was demonstrated; items that varied between countries and from the composite may reflect unique cultural response patterns or differences in translation. Scoring algorithms based on the Rasch model for each country were superior to the current Likert scoring in tests of relative validity (RV) in discriminating among age groups in all countries. In relation to the Likert PF-10 scoring (RV = 1.00), scores estimated using the Rasch rating scale model achieve a median RV of 1.31 (range: 1.01-1.59), while the Rasch partial credit model attained a median RV of 1.44 (range: 1.01-2.23). Rasch models hold good potential for improving health status measures, estimating individual scores when responses to scale items are missing, and equating scores across countries.

A Content Validity Study of the Pediatric Evaluation of Disability Inventory

The Pediatric Evaluation of Disability (PEDI) was developed as a comprehensive functional assessment instrument for pediatric rehabilitation. The PEDI samples content in the domains of self-care, mobility, toileting, and social cognition. These content domains are evaluated by three separate scales: 1) functional skills/behaviors, 2) caregiver assistance of complex activities, and 3) environmental modifications and equipment. The PEDI can be used as a parent report/structured interview instrument or by professionals observing the childs functional behavior in a hospital, outpatient, or educational setting. This article describes the development edition (pilot) of the PEDI and includes a report of a content validity study with 31 expert reviewers. Overall, the content validity and feasibility of the PEDI were supported. Revisions made in the standardization version of the PEDI based on the content validity study are discussed.

Comparison of Rasch and Summated Rating Scales Constructed from SF-36 Physical Functioning Items in Seven Countries: Results from the IQOLA Project

Rasch models for polytomous items were used to assess the scaling assumptions and compare item response patterns in the 10-item SF-36 physical functioning scale (PF-10) for general population respondents in Denmark, Germany, Italy, the Netherlands, Sweden, the United Kingdom, and the United States. The Rasch model of physical functioning developed in the United States was compared to models for other countries, and each country was compared to a multinational composite. Strong scale congruence across the seven countries was demonstrated; items that varied between countries and from the composite may reflect unique cultural response patterns or differences in translation. Scoring algorithms based on the Rasch model for each country were superior to the current Likert scoring in tests of relative validity (RV) in discriminating among age groups in all countries. In relation to the Likert PF-10 scoring (RV = 1.00), scores estimated using the Rasch rating scale model achieve a median RV of 1.31 (range: 1.01-1.59), while the Rasch partial credit model attained a median RV of 1.44 (range: 1.01-2.23). Rasch models hold good potential for improving health status measures, estimating individual scores when responses to scale items are missing, and equating scores across countries.

Prospective Evaluation of the AM-PAC-CAT in Outpatient Rehabilitation Settings

Background and Purpose The purpose of this study was to prospectively evaluate the practical and psychometric adequacy of the Activity Measure for Post-Acute Care (AM-PAC) “item bank” and computerized adaptive testing (CAT) assessment platform (AM-PAC-CAT) when applied within orthopedic outpatient physical therapy settings. Method This was a prospective study with a convenience sample of 1,815 patients with spine, lower-extremity, or upper-extremity impairments who received outpatient physical therapy in 1 of 20 outpatient clinics across 5 states. The authors conducted an evaluation of the number of items used and amount of time needed to complete the CAT assessment; evaluation of breadth of content coverage, item exposure rate, and test precision; as well as an assessment of the validity and sensitivity to change of the score estimates. Results Overall, the AM-PAC-CATs Basic Mobility scale demonstrated excellent psychometric properties while the Daily Activity scale demonstrated less adequate psychometric properties when applied in this outpatient sample. The mean length of time to complete the Basic Mobility scale was 1.9 minutes, using, on average, 6.6 items per CAT session, and the mean length of time to complete the Daily Activity scale was 1.01 minutes, using on average, 6.8 items. Background and Conclusion Overall, the findings are encouraging, yet they do reveal several areas where the AM-PAC-CAT scales can be improved to best suit the needs of patients who are receiving outpatient orthopedic physical therapy of the type included in this study.