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- Common metric; DASH; Disability and Health; HAQ; International Classification of Functioning; Multidimensional HAQ; PROMIS-SF; Rasch measurement model; Scale banking; WHODAS 2.0; WOMAC. (1)
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Objective: Functioning is an important outcome to measure in cohort studies. Clear and operational outcomes are needed to judge the quality of a cohort study. This paper outlines guiding principles for reporting functioning in cohort studies and addresses some outstanding issues.
Design: Principles of how to standardize reporting of data from a cohort study on functioning, by deriving scores that are most useful for further statistical analysis and reporting, are outlined. The Swiss Spinal Cord Injury Cohort Study Community Survey serves as a case in point to provide a practical application of these principles.
Methods and Results: Development of reporting scores must be conceptually coherent and metrically sound. The International Classification of Functioning, Disability and Health (ICF) can serve as the frame of reference for this, with its categories serving as reference units for reporting. To derive a score for further statistical analysis and reporting, items measuring a single latent trait must be invariant across groups. The Rasch measurement model is well suited to test these assumptions.
Conclusion: Our approach is a valuable guide for researchers and clinicians, as it fosters comparability of data, strengthens the comprehensiveness of scope, and provides invariant, interval-scaled data for further statistical analyses of functioning.
Background
Limitations in upper limb functioning are common in Musculoskeletal disorders and the Disabilities of the Arm, Shoulder and Hand scale (DASH) has gained widespread use in this context. However, various concerns have been raised about its construct validity and so this study seeks to examine this and other psychometric aspects of both the DASH and QuickDASH from a modern test theory perspective.
Methods
Participants in the study were eligible if they had a confirmed diagnosis of Rheumatoid Arthritis (RA). They were mailed a questionnaire booklet which included the DASH. Construct validity was examined by fit to the Rasch measurement model. The degree of precision of both the DASH and QuickDASH were considered through their Standard Error of Measurement (SEM).
Results
Three hundred and thirty-seven subjects with confirmed RA took part, with a mean age of 62.0 years (SD12.1); 73.6% (n = 252) were female. The median standardized score on the DASH was 33 (IQR 17.5–55.0). Significant misfit of the DASH and QuickDASH was observed but, after accommodating local dependency among items in a two-testlet solution, satisfactory fit was obtained, supporting the unidimensionality of the total sets and the sufficiency of the raw (ordinal or standardized) scores.
Conclusion
Having accommodated local response dependency in the DASH and QuickDASH item sets, their total scores are shown to be valid, given they satisfy the Rasch model assumptions. The Rasch transformation should be used whenever all items are used to calculate a change score, or to apply parametric statistics within an RA population.
Significance and innovations
Most previous modern psychometric analyses of both the DASH and QuickDASH have failed to fully address the effect of a breach of the local independence assumption upon construct validity.
Accommodating this problem by creating ‘super items’ or testlets, removes this effect and shows that both versions of the scale are valid and unidimensional, as applied with a bi-factor equivalent solution to an RA population.
The Standard Error of Measurement of a scale can be biased by failing to take into account the local dependency in the data which inflates reliability and thus making the SEM appear better (i.e. smaller) than the true value without bias.
Objective
Our aim was to specify the requirements of an architecture to serve as the foundation for standardized reporting of health information and to provide an exemplary application of this architecture.
Methods
The World Health Organization’s International Classification of Functioning, Disability and Health (ICF) served as the conceptual framework. Methods to establish content comparability were the ICF Linking Rules. The Rasch measurement model, as a special case of additive conjoint measurement, which satisfies the required criteria for fundamental measurement, allowed for the development of a common metric foundation for measurement unit conversion. Secondary analysis of data from the North Yorkshire Survey was used to illustrate these methods. Patients completed three instruments and the items were linked to the ICF. The Rasch measurement model was applied, first to each scale, and then to items across scales which were linked to a common domain.
Results
Based on the linking of items to the ICF, the majority of items were grouped into two domains, Mobility and Self-care. Analysis of the individual scales and of items linked to a common domain across scales satisfied the requirements of the Rasch measurement model. The measurement unit conversion between items from the three instruments linked to the Mobility and Self-care domains, respectively, was demonstrated.
Conclusions
The realization of an ICF-based architecture for information on patients’ functioning enables harmonization of health information while allowing clinicians and researchers to continue using their existing instruments. This architecture will facilitate access to comprehensive and consistently reported health information to serve as the foundation for informed decision-making.
Metric properties of the Spinal Cord Independence Measure - Self Report in a community survey
(2016)
Objective: The Spinal Cord Independence Measure – Self Report (SCIM-SR) is a self-report instrument for assessing functional independence of persons with spinal cord injury. This study examined the internal construct validity and reliability of the SCIM-SR, when administered in a community survey, using the Rasch measurement model.
Methods: Rasch analysis of data from 1,549 individuals with spinal cord injury who completed the SCIM-SR.
Results: In the initial analysis no fit to the Rasch model was achieved. Items were grouped into testlets to accommodate the substantial local dependency. Due to the differential item functioning for lesion level and degree, spinal cord injury-specific sub-group analyses were conducted. Fit to the Rasch model was then achieved for individuals with tetraplegia and complete paraplegia, but not for those with incomplete paraplegia. Comparability of ability estimates across sub-groups was attained by anchoring all sub-groups on a testlet.
Conclusion: The SCIM-SR violates certain assumptions of the Rasch measurement model, as shown by the local dependency and differential item functioning. However, an intermediate solution to achieve fit in 3 out of 4 spinal cord injury sub-groups was found. For the time being, therefore, it advisable to use this approach to compute Rasch-transformed SCIM-SR scores.
Objective
To demonstrate the influence and added value of a Standardized Assessment and Reporting System (StARS) upon the reporting of functioning outcomes for national rehabilitation quality reports. A StARS builds upon an ICF-based (International Classification of Functioning, Disability and Health) and interval-scaled common metric.
Design
Comparison of current ordinal-scaled Swiss national rehabilitation outcome reports including an expert-consensus-based transformation scale with StARS-based reports through descriptive statistical methods and content exploration of further development areas of the reports with relevant ICF Core Sets.
Setting
Swiss national public rehabilitation outcome quality reports on the clinic level.
Participants
A total of 29 Swiss rehabilitation clinics provided their quality report datasets including 18 047 patients.
Interventions
Neurological or musculoskeletal rehabilitation.
Main outcome measures
Functional Independence Measure™ or Extended Barthel Index.
Results
Outcomes reported with a StARS tended to be smaller but more precise than in the current ordinal-scaled reports, indicating an overestimation of achieved outcomes in the latter. The comparison of the common metric’s content with ICF Core Sets suggests to include ‘energy and drive functions’ or ‘maintaining a basic body position’ to enhance the content of functioning as an indicator.
Conclusions
A StARS supports the comparison of outcomes assessed with different measures on the same interval-scaled ICF-based common metric. Careful consideration is needed whether an ordinal-scaled or interval-scaled reporting system is applied as the magnitude and precision of reported outcomes is influenced. The StARS’ ICF basis brings an added value by informing further development of functioning as a relevant indicator for national outcome quality reports in rehabilitation.
Background: The Extended Barthel Index (EBI), consisting of the original Barthel Index plus 6 cognitive items, provides a tool to monitor patients’ outcomes in rehabilitation. Whether the EBI provides a unidimensional metric, thus can be reported as a valid sum-score, remains to be examined.
Objective: To examine whether the EBI can be reported as unidimensional interval-scaled metric for neurological and musculoskeletal rehabilitation.
Methods: Rasch analysis of a calibration sample of 800 cases from neurological or musculoskeletal rehabilitation in 2016 in Switzerland.
Results: In the baseline analysis no fit to the Rasch Model was achieved. When accommodating local dependencies with a testlet approach satisfactory fit to the Rasch Model was achieved, and an interval scale transformation table was created.
Conclusion: The results support the reporting of adapted EBI total scores for both rehabilitation groups by applying the interval scaled transformation table presented in this study.
Abstract
Objective: Since the 1990s the Functional Independence Measure (FIM™) was believed to measure 2 different constructs, represented by its motor and cognitive subscales. The practice of reporting FIM™ total scores, together with recent developments in the understanding of the influence of locally dependent items on fit to the Rasch model, raises the question of whether the FIM™ 18-item version can be reported as a unidimensional interval-scaled metric.
Design: Rasch analysis of the FIM™ using testlet approaches to accommodate local response dependency.
Patients: A calibration sample containing 946 cases of data from 11,103 patients undergoing neurological or musculoskeletal rehabilitation in Switzerland in 2016.
Results: Baseline analysis and the traditional testlet approach showed no fit with the Rasch model. When items were grouped into 2 testlets, fit to the Rasch model was achieved, indicating unidimensionality across all 18 items. A transformation table to convert FIM™ raw ordinal scores to the corresponding Rasch interval scaled values was created.
Conclusion: This study provides evidence that FIM™ total scores represent a unidimensional set of items, supporting their use in clinical practice and outcome reporting when applying the respective transformation table. This provides a basis for standardized reporting of functioning.
Lay Abstract
The aim of this study was to look in detail at the FIM™, an assessment tool often used for patients undergoing rehabilitation. Some users report the FIM™ as 2 scores: one related to motor tasks, the other to cognitive tasks; others recommend reporting it as a single score including both motor and cognitive tasks. This study explored whether it is statistically meaningful to sum all the points into a single FIM™ total score. The results support the current practice of summing the points into a single total score for patients undergoing musculo-skeletal and neurological rehabilitation. The results also allowed an interval scale to be derived from the FIM™, enabling a broad range of calculations to be made using the FIM™ score, such as calculating the change in FIM™ outcomes from the time a patient is admitted to a rehabilitation clinic until their discharge.
Background: The International Classification of Functioning, Disability and Health is the international standard for describing and monitoring functioning. While the categories, the units of the classification, were not designed with measurement in mind, the hierarchical structure of the classification lends itself to the possibility of summating categories into some higher order domain. Focusing on the chapters of d4 Mobility, d5 Self-Care and d6 Domestic Life, this study seeks to ascertain if qualifiers rating of categories (0-No problem to 4-Complete problem) within those chapters can be summated, and whether such derived measurement is consistent with estimates obtained from well-known instruments which purport to measure the same constructs.
Methods: The current study applies secondary analysis to data previously collected in the context of validating Core Sets for stroke, rheumatoid arthritis, and osteoarthritis. Data included qualifier-based ratings of the categories in the Core Sets, and the physical functioning sub-scale of the Short-Form 36, and the World Health Organization Disability Assessment Schedule 2.0. To examine qualifier-comparator scale item agreement Kappa statistics were used. To identify whether appropriate gradients of the comparator scales were observed across qualifier levels, an Independent Sample Median Test of the ordinal scores was deployed. To investigate the internal validity of the summated ICF categories, the Rasch model was applied.
Results: Data from 2,927 subjects from Europe, Australasia, Middle East and South America were available for analysis; 36.3% had experienced a stroke, 35.8% osteoarthritis, and 27.9% had rheumatoid arthritis. The items from the Short-Form 36 could not match directly the qualifier categories as the former had only 3 response options. The Kappa between World Health Organization Disability Assessment Schedule 2.0 items and categories was low. For all qualifiers, a significant (<0.001) overall gradient was observed across the comparator scales. Only in few of the World Health Organization Disability Assessment Schedule 2.0 items could no discrete level be detected. The aggregation of the qualifiers at the Chapter and higher order levels mostly revealed fit to the Rasch model. Almost all ICF qualifiers showed ordered thresholds suggesting that the current structure and response options of the qualifiers worked as intended.
Conclusions: The findings of this study provide supporting evidence for the use of the professionally rated categories and associated qualifiers to measure functioning.
Implication for Rehabilitation
- This study provides evidence that functioning data can be collected directly with the International Classification of Functioning, Disability and Health (ICF) by using the ICF categories as items and the ICF qualifiers as rating scale.
- The findings of this study show the aggregated ratings of ICF categories from the chapters d4 Mobility, d5 Self-care, and d6 Domestic life capture a broader spectrum of the construct than the corresponding summated items from the SF36-Physical Function sub-scale and the corresponding items of the World Health Organization Disability Assessment Schedule 2.0.
- This study illustrates the potential of building quantitative measurement by aggregating ICF categories and their qualifier ratings into meaningful domains.
BACKGROUND: In clinical practice and research a variety of clinical data collection tools are used to collect information on people’s functioning for clinical practice and research and national health information systems. Reporting on ICF-based common metrics enables standardized documentation of functioning information in national health information systems. The objective of this methodological note on applying the ICF in rehabilitation is to demonstrate how to report functioning information collected with a data collection tool on ICF-based common metrics. We first specify the requirements for the standardized reporting of functioning information. Secondly, we introduce the methods needed for transforming functioning data to ICF-based common metrics. Finally, we provide an example.
METHODS: The requirements for standardized reporting are as follows: 1) having a common conceptual framework to enable content comparability between any health information; and 2) a measurement framework so that scores between two or more clinical data collection tools can be directly compared. The methods needed to achieve these requirements are the ICF Linking Rules and the Rasch measurement model. Using data collected incorporating the 36-item Short Form Health Survey (SF-36), the World Health Organization Disability Assessment Schedule 2.0 (WHODAS 2.0), and the Stroke Impact Scale 3.0 (SIS 3.0), the application of the standardized reporting based on common metrics is demonstrated.
RESULTS: A subset of items from the three tools linked to common chapters of the ICF (d4 Mobility, d5 Self-care and d6 Domestic life), were entered as “super items” into the Rasch model. Good fit was achieved with no residual local dependency and a unidimensional metric. A transformation table allows for comparison between scales, and between a scale and the reporting common metric.
CONCLUSIONS: Being able to report functioning information collected with commonly used clinical data collection tools with ICF-based common metrics enables clinicians and researchers to continue using their tools while still being able to compare and aggregate the information within and across tools.
Objective: Functioning is an important outcome for rheumatoid arthritis (RA) management. Heterogeneity of respective patient-reported outcome measures (PROMs) challenges direct comparisons between their results. This study aimed to standardize reporting of such PROMs measuring functioning in RA to facilitate comparability.
Methods: Common Item Non-Equivalent Groups Design (NEAT) with the Health Assessment Questionnaire (HAQ) as a common scale across data sets from various countries (incl. UK, Turkey and Germany) to establish a common metric. Other PROMs included are the Physical Function items of the Multidimensional Health Assessment Questionnaire (MDHAQ), Disabilities of Arm, Shoulder and Hand (DASH), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), World Health Organization Disability Assessment Schedule Version 2.0 (WHODAS 2.0), and four short forms (20, 10, 6, and 4 physical function items) from the Patient-Reported Outcomes Measurement Information System (PROMIS). As the HAQ includes mobility, self-care and domestic life items, this study focuses on these three domains. PROMs were described using Standard Error of Measurement (SEM) and Smallest Detectable Difference (SDD). Rasch Measurement model was used to create the common metric.
Results: Range of SEM is 0.2 (MDHAQ) to 7.4 (SF36-PF). SDD revealed a range from 9.7 % (WOMAC-RAT) to 33.5 % (WHODAS-PF). PROMs co-calibration revealed fit to the Rasch measurement model. A transformation table was developed to allow exchange between PROMs scores.
Discussion: Scores between the Daily Activity PROMs commonly used in RA can now be compared. Factors such as SEM and SDD help determine choice of PROM in clinical practice and research.
Keywords: Common metric; DASH; Disability and Health; HAQ; International Classification of Functioning; Multidimensional HAQ; PROMIS-SF; Rasch measurement model; Scale banking; WHODAS 2.0; WOMAC.