Elsevier

Journal of Clinical Epidemiology

Volume 62, Issue 9, September 2009, Pages 912-921.e3
Journal of Clinical Epidemiology

International Classification of Functioning Disability and Health
Items from patient-oriented instruments can be integrated into interval scales to operationalize categories of the International Classification of Functioning, Disability and Health

https://doi.org/10.1016/j.jclinepi.2008.04.011Get rights and content

Abstract

Objective

To exemplify the construction of interval scales for specified categories of the International Classification of Functioning, Disability and Health (ICF) by integrating items from a variety of patient-oriented instruments.

Study Design and Setting

Psychometric study using data from a convenience sample of 122 patients with rheumatoid arthritis. Patients completed six different patient-oriented instruments. The contents of the instrument items were linked to the ICF. Rasch analyses for ordered-response options were used to examine whether the instrument items addressing the ICF category b130: Energy and drive functions constitute a psychometrically sound interval scale.

Results

Nineteen items were linked to b130: Energy and drive functions. Sixteen of the 19 items fit the Rasch model according to the chi-square (χ2) statistic (χ2df=32 = 38.25, P = 0.21) and the Z-fit statistic (ZMean = 0.451, ZSD = 1.085 and ZMean = −0.223, ZSD = 1.132 for items and persons, respectively). The Person Separation Index rβ was 0.93.

Conclusion

The ICF category interval scales to operationalize single ICF categories can be constructed. The original format of the items included in the interval scales remains unchanged. This study represents a step forward in the operationalization and future implementation of the ICF.

Introduction

Functioning and disability are universal human experiences [1], [2] that are at the core of medicine [3] and public health [4]. They are also of essential relevance in sectors, such as labor, education, and social affairs [5].

In medicine, the management of limitations in functioning complements medical and surgical care throughout the service continuum, from the acute to the community health care situation [6]. Improving or maintaining functioning or the prevention of disability is becoming one of the most urgent outcomes in public health [7]. In the labor, education, and social affairs sectors, planning and implementation of preventative actions are only viable if the needs of people experiencing, or likely to experience, disability are considered [5]. Accordingly, concepts, classifications, and measures of functioning and disability are of great interest and importance across professional disciplines and sectors.

With the International Classification of Functioning, Disability and Health (ICF) [8], the WHO, for the first time, provides a universal and globally accepted framework and classification to describe the full range of human functioning and disability that may be affected by a health condition [9]. The ICF model identifies three components of the dimension functioning, namely body functions and structures, activities, and participation. Problems or difficulties in these components are called impairments, activity limitations, and participation restrictions, that is, they are components of the dimension disability. Dimensions of functioning and of disability are both affected by interactions between health conditions and contextual factors (environmental and personal).

The components of body functions and structures, activities and participation, and environmental factors (a list of personal factors awaits further research and development) are classified based on the ICF categories. The ICF contains a total of 1,424 categories that are mutually exclusive and organized within a hierarchically nested structure with up to four different levels. The ICF categories are denoted by unique alphanumeric codes with which it is possible to classify, measure, and describe functioning and disability, both on the individual and population levels.

Because the ICF categories are always accompanied by a short definition and inclusions and exclusions, as appropriate, the information on the aspects of functioning can be reported unambiguously and compared based on ICF categories [10], [11]. Examples of ICF categories, with their definitions, inclusions, and exclusions, can be found in Table A1 (available on the journal's website at www.elsevier.com). An example of the hierarchically nested structure is presented in the following:

  • “b1 Mental functions” (first/chapter level)

  • “b130 Energy and drive functions” (second level)

  • “b1301 Motivation” (third level)

In principle, there are two approaches to measure a specified ICF category, that is, to quantify the extent of variation therein. The first is to use the so-called ICF qualifier as an expert rating scale ranging from 0 to 4 (Table A2 [available on the journal's website at www.elsevier.com]). With this approach, impairments, activity limitations, participation restrictions, and contextual factors are directly rated according to established coding guidelines [8]. However, as in any rating scale, the expert can access whatever sources of information are available [12].

The second approach is to use information obtained with a clinical test that includes standardized expert and technical examinations, or a patient-oriented instrument that includes patient- and proxy-reported, self-administered, or interview-administered questionnaires, and to transform this information into the ICF qualifier. In a first step, a clinical test or patient-oriented instrument is linked to the ICF based on established linking rules [13]. In a second step, the scores obtained with a clinical test or a patient-oriented instrument are transformed to the ICF qualifier.

This second approach has the advantage that information already available can be transformed into the standard language of the ICF, to be understood by all interested professionals irrespective of their disciplines or the sectors (e.g., health, labor, or education) in which they are involved.

The transformation to the ICF qualifier is straightforward when interval-scaled clinical tests or patient-oriented instruments, which comprehensively and uniquely cover the content of a respective ICF category, are readily available. For example, the visual analog scale (VAS) for the assessment of pain can be linked, in a first step, to the ICF category b280: Sensation of pain. In a second step, the values of the VAS-Pain can be transformed into an ICF qualifier in a straightforward manner, because it represents a 100-mm interval scale marked as “no pain” at one end and as ”worst pain” at the other [14]. Considering the percentage values of the ICF qualifier of Table A2 (available on the journal's website at www.elsevier.com), a person marking a level of pain between 0 and 4 mm would receive qualifier 0 in the ICF category b280: Sensation of pain; between 5 and 24 mm, qualifier 1; between 25 and 49 mm, qualifier 2; between 50 and 95 mm, qualifier 3; and between 96 and 100 mm, qualifier 4.

If there are no readily available clinical tests or patient-oriented instruments, a third approach can be developed. One may consider using parts of clinical test batteries or selected items of patient-oriented instruments that cover a specified ICF category. Thus, an ICF category interval scale can be constructed to serve as an interface between the clinical test or patient-oriented instrument and the ICF qualifier.

Established linkage rules [13], [15] can be used to identify suitable parts of clinical tests and items of patient-oriented instruments. Rasch or Item Response Theory (IRT) models [16] can be applied to construct interval scales. However, the complete process of how to develop ICF category interval scales and how they can serve as an interface have not been described to date.

The objective of this article was to exemplify the construction of interval scales for specified ICF categories by integrating items from a variety of widely used patient-oriented instruments, which were filled in by a convenience sample of rheumatoid arthritis (RA) patients. The specific aims are to:

  • 1.

    identify candidate items from a range of patient-oriented instruments that address specific ICF categories, and

  • 2.

    estimate the extent to which selected items that address the ICF category “Energy and drive functions” form a unidimensional, ordered interval scale.

Section snippets

Study design

The psychometric study used data from a convenience sample of patients with RA that was collected in a cross-sectional study conducted at the University Hospital Maastricht, The Netherlands. Patients were asked to fill in a number of patient-oriented instruments for reasons other than this psychometric study.

The study protocol and informed consent forms of the cross-sectional study were approved by the Ethics Committee of the University Hospital in Maastricht. Inclusion criteria for patients

Study population

The demographic and RA-related characteristics of the convenience sample of 122 patients are shown in Table 1.

Identification of candidate items

Table 2 shows the results of the evaluation of the linkage procedure as the percentage of observed agreement, kappa statistics, and bootstrapped CIs for all different levels of the ICF. None of the 95% CIs encloses 0, indicating that the agreement exceeded chance.

The second-level ICF category b130: Energy and drive functions was the ICF category to which the largest number of items were

Discussion

We have illustrated how the value on the ICF qualifier can be estimated based on the interval scales developed for specified ICF categories by integrating the items from patient-oriented instruments. The original format of the items used to construct the ICF category interval scale remained unchanged. Thus, it is possible to use the information provided by items within the context of their original instruments and, at the same time, within the context of the ICF. This application can be

Acknowledgments

The authors thank Heinrich Gall, Alicia Garza, Andrea Glässel, and Michaela Kirschneck for their support in conducting this study, and Pieter Lozekoot and Jos Ramaker for collecting the data.

This study was partially supported by a grant from the European League Against Rheumatism (EULAR).

References (57)

  • G. Stucki et al.

    Rationale and principles of early rehabilitation care after an acute injury or illness

    Disabil Rehabil

    (2005)
  • G. Stucki et al.

    The International Classification of Functioning, Disability and Health (ICF): a unifying model for the conceptual description of the rehabilitation strategy

    J Rehabil Med

    (2007)
  • International Classification of Functioning, Disability and Health: ICF

    (2001)
  • G. Stucki et al.

    Value and application of the ICF in rehabilitation medicine

    Disabil Rehabil

    (2002)
  • M.E. Finger et al.

    Identification of intervention categories for physical therapy, based on the international classification of functioning, disability and health: a Delphi exercise

    Phys Ther

    (2006)
  • H.P. Rentsch et al.

    The implementation of the “International Classification of Functioning, Disability and Health” (ICF) in daily practice of neurorehabilitation: an interdisciplinary project at the Kantonsspital of Lucerne, Switzerland

    Disabil Rehabil

    (2003)
  • I. McDowell

    Measuring health: a guide to rating scales and questionnaires

    (2006)
  • A. Cieza et al.

    ICF linking rules: an update based on lessons learned

    J Rehabil Med

    (2005)
  • S.L. Wallerstein

    Scaling clinical pain and pain relief

  • A. Cieza et al.

    Linking health-status measurements to the international classification of functioning, disability and health

    J Rehabil Med

    (2002)
  • D. Andrich

    Controversy and the Rasch model: a characteristic of incompatible paradigms?

    Med Care

    (2004)
  • G.J. Tijhuis et al.

    The validity of the Rheumatoid Arthritis Quality of Life (RAQoL) questionnaire

    Rheumatology

    (2001)
  • J.F. Fries et al.

    Measurement of patient outcome in arthritis

    Arthritis Rheum

    (1980)
  • J.E. Ware et al.

    The MOS 36-item short-form health survey (SF-36). A. Conceptual framework and item selection

    Med Care

    (1992)
  • Euroqol—a facility for the measurement of health-related quality of life

    Health Policy

    (1990)
  • Center for Epidemiologic Studies Depression Scale (CES-D)

    (1971)
  • A. Cieza et al.

    Content comparison of health-related quality of life (HRQOL) instruments based on the international classification of functioning, disability and health (ICF)

    Qual Life Res

    (2005)
  • J. Cohen

    A coefficient of agreement for nominal scales

    Educ Psychol Meas

    (1960)
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