Review Article
The dilemma of measuring perceived health status in the context of disability

https://doi.org/10.1016/j.dhjo.2008.12.003Get rights and content

Abstract

Background

Advances in the conceptual differentiation of health from disability have not been incorporated in popular measures of perceived health status. The inclusion of function in the measurement of health presents a dilemma for researchers assessing the perceived health of people with functional limitations.

Objectives

The purposes of the present paper are to identify this problem in health measurement, describe its implications for disability and health researchers, and outline potential strategies for future measure development of perceived health status.

Methods

Reflecting the International Classification of Function, Disability, and Health, distinctions among the concepts of health, function, and disability are reviewed. Implications of confounded health measurement are discussed in terms of monitoring health status, assessing health disparities, using health as a mediator or moderator of other outcomes, and assessing effectiveness of interventions. The problem of function confounded with health measurement is illustrated with findings using the SF-36 with persons with spinal cord injury.

Results

Recommendations are provided for developing function-neutral measures of perceived health status.

Conclusion

New measures of perceived health status are needed that do not confound function with health.

Section snippets

Differentiating Health, Function, and Disability

Understanding the genesis of many current HRQOL measures provides a basis for understanding the current problem of health measurement that is confounded with function. The early roots of perceived health status measurement occurred in a time that preceded contemporary distinctions among health, function, and disability. Historically, disabilities were considered equivalent to chronic health conditions. This perspective is still evident in studies that combine respondents with chronic health

Need for a function-neutral HRQOL measure

Until the early 1970s, health researchers primarily understood the health of populations and research samples in terms of mortality (e.g., how many people died? at what ages did they die?) and morbidity (e.g., how many people are sick? How many people experience symptoms?). This traditional approach to conceptualizing health is still in use [43]. During the last 40 years, health measurement expanded to include measures of perceived health or health status [44], [45]. As a result, a new category

Cognition and Self-Report

There is general agreement that health related quality of life is an internal experience requiring self-report as the form of data collection [10], [11], [40]. A number of models have been proposed that incorporate the process of interpreting questions, memory and recall, and formulating a response [49], [50], [51], [52], [53]. For example, the internal experience of HRQOL is influenced by individuals’ expectations and these expectations can change based on life experiences [54], [55]. Research

Addressing Functional Biases

Items in a measure of perceived health status should demonstrate neutrality relative to functional abilities of respondents. Function neutrality still allows for mean differences between groups, but these differences should represent characteristics of health such as pain, fatigue or depression and not elements of independent function. Development of a function-neutral measure of health would require surmounting three core challenges: (1) operationalizing the concept of function as distinct

Identifying and Neutralizing Functional Bias

In response to the increasing attention given to the constructs of health and function in disability research, members of the ICF Research Branch mapped the items of six popular measures of HRQOL onto the framework of the ICF [64]. Expert judgment determined the allocations. Their analyses clearly demonstrate the great variability across HRQOL measures in emphasis on “body function” versus “activities and participation.” The SF-36 crosses both constructs (14 items in body function, 24

Validation of Function-Free Items

Differential Item Functioning (DIF) analysis is one method for assessing functional bias at the item level while still allowing for mean level differences between groups. Item level DIF scores are computed by calculating the item mean for a disability sample, partialling out the sample's mean score on the domain of interest. This disability sample score is then compared with the corresponding item score for the normative sample which has been similarly adjusted by partialling out the normative

Conclusion

The conceptual distinctions between health and function that have emerged over the past two decades have revealed a measurement dilemma for disability and health researchers. Most current research measures of perceived health status or health related quality of life confound measurement of health with measurement of function. This confounding contributes to a number of problems in calibration, measurement error, respondent burden and erroneous research conclusions. Their use can lead to

Acknowledgments

The RRTC Expert Panel on Health Measurement includes Vincent Campbell, PhD, Centers for Disease Control and Prevention; Brad Cardinal, PhD, Oregon State University; Charles Drum, JD, PhD, Oregon Health & Science University; Glenn Fujiura, PhD, University of Illinois at Chicago; Trevor Hall, PhD, Oregon Health & Science University, Willi Horner-Johnson, PhD, Oregon Health & Science University; Gloria Krahn, PhD, Oregon Health & Science University; Margaret Nosek, PhD, Baylor College of Medicine;

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    The authors have no financial disclosures or conflicts of interest to declare.

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