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Geyh, Szilvia (2007): Connecting perspectives on stroke disability: The measurement and the classification approach. Dissertation, LMU München: Faculty of Medicine
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Abstract

1. Background Stroke is a frequently occurring condition and a common cause of death and disability. Many stroke survivors are facing long-term disability. The consequences of stroke on patients’ functioning are usually complex and heterogeneous. Precise knowledge of patients’ stroke related disability is necessary in health services provision and research. Clinical stroke management, but also epidemiological and clinical research, depend on the careful detection of functioning problems, as well as resources, in patients with stroke. Two conceptual approaches to describe patients’ disability can be distinguished: the health status measurement and the classification approach. Health status measures, like standardized performance tests, rating scales, and questionnaires are used to operationalize and to assess patients’ burden of disease, functioning and health. The classification approach towards the description of patients’ health state is represented by the World Health Organization’s International Classification of Functioning, Disability and Health (ICF). The ICF provides a comprehensive conceptual framework and a unified standardized language to describe health and health related states, both at the individual, as well as at population levels. To enhance the applicability of the classification, ICF Core Sets for specific health conditions have been developed in an evidence based and consensus based process. The ICF Core Sets for Stroke are selections of salient ICF categories out of the whole classification, which describe the spectrum of problems in stroke patients’ functioning based on the universal language of the ICF. The ICF Core Sets for Stroke represent the practical implementation of the classification approach in clinical practice and research. The two approaches to represent stroke related disability, the health status measurement and the classification approach, can be regarded as complementary principles. From the classification perspective, the ICF and the ICF Core Sets can serve as standards to define what to measure. From the perspective of health status measurement the question how to measure can be answered. An explicit connection between the two approaches can be established by the so-called linking method. Thereby, using the ICF’s category system the contents of measures can be mapped, explored and compared in a standardized, transparent and straightforward way. The linking method can be useful for various purposes. The application of the linking method along with the ICF Core Sets constitutes a new approach for examining health status measures’ content validity. However, beyond content validity, meaningful measurement essentially depends on the psychometric quality of the applied instruments. Techniques based on modern test theory, especially Rasch analysis, are increasingly adopted to ensure instruments’ psychometric properties. 2. Objectives In the following, the doctoral thesis is subdivided into four parts. The first three parts present different studies performed to pursue the objectives named below. Each of the three studies contains a respective discussion section referring to the results of the study. The fourth part of the doctoral thesis refers to aim four, namely the discussion of the relationship between the methods presented in the previous three parts. The current doctoral thesis aims (1) to illustrate, how the connection between the health status measurement approach and the classification approach can be established by the application of the linking method, (2) to demonstrate, how this approach can be used to select health status measures based on their content validity, (3) to show, how the psychometric features of health status measures can be examined based on Rasch analyses, and (4) to discuss the relationship between the demonstrated methods in the context of the connection of the health status measurement and the classification approach. 3. Applying the linking method: Content comparison of patient-centered health status measures used in stroke based on the International Classification of Functioning, Disability and Health (ICF) The first study, “Content comparison of patient-centered health status measures used in stroke based on the International Classification of Functioning, Disability and Health (ICF)” illustrates the application of the linking method in stroke measurement. The objective of this study was to examine and to compare the contents of patient-centred health status measures used in stroke. The specific aims of the study included the identification of generic and condition-specific patient-centred health status measures applied in stroke patients, the examination of the contents of the single measures based on their linking to the ICF, and the comparison of the contents of generic and stroke-specific measures. A systematic literature review was conducted to identify current generic and condition-specific patient-centred health status measures applied in stroke. The most frequently used instruments were selected. The contents of the selected measures were examined by linking the concepts within the instruments’ items to the ICF. Six generic and seven stroke-specific health status measures were selected. Within the selected instruments 979 concepts were identified. 200 different ICF categories were used to map these concepts. No single ICF category is contained in all instruments. Out of the total 200 different ICF categories used, 77 (40%) applied to only one of the 13 selected measures. Overall, the most frequently used category is b152 emotional functions’ contained in 53 items from 10 instruments. Stroke-specific measures more often address mental functions, while the selected generic instruments more often include Environmental Factors. The study provides an overview on current patient-centered health status measures in stroke and their covered contents. The results of the content comparison provide valuable information to facilitate and to account for the selection of appropriate instruments for specific purposes in clinical as well as research settings. 4. Selecting health status measures based on content validity: Comparison of stroke-specific health status measures with the Comprehensive ICF Core Set for Stroke The aim of the second study is to demonstrate how the ICF as a fundamental reference can be used to select health status measures according to their content validity. The specific aims are (1) to examine the content validity of the selected stroke-specific health status measures by comparing them with the Comprehensive ICF Core Set for Stroke, and (2) to discuss the selection of measures based on their coverage of the ICF Core Set. Taking the results from the previous study, the seven stroke-specific patient-centered health status measures are involved in the current analyses and compared to the Comprehensive ICF Core Set for Stroke. Descriptive frequency analyses are conducted to indicate the instruments’ bandwidth and specificity of content coverage regarding the ICF Core Set. 67 (52%) out of the 130 categories of the ICF Core Set are covered by at least one of the examined instruments. The single measures cover in total between 29% and 14% of the Comprehensive ICF Core Set for Stroke. Overall, 31 categories of the ICF Core Set are measured at the more specific 3rd and 4th levels by at least one of the seven instruments. All instruments cover Activity and Participation and Body Functions, but only two instruments address Environmental Factors. No categories of the ICF component Body Structures are contained in the examined instruments. In contrast the Comprehensive ICF Core Set for Stroke contains categories from all ICF components. The Quality of Life Instrument for Young Haemorrhagic Stroke Patients (HSQuale), the Stroke-specific Quality of Life Scale (SSQoL), and the Stroke Impact Scale(SIS) represent the top three instruments according to bandwidth as well as specificity of content coverage. The comparison of instruments against the Comprehensive ICF Core Set for Stroke can be used to characterize and compare measures’ content validity. The examination and comparison of patient-centered health status measures’ content validity accounting for the bandwidth and the specificity of content coverage can serve as a first step of selecting a measure. However, further features of the measures have to be considered. Especially, their psychometric properties have to be carefully examined to accomplish the well-founded choice of appropriate measures to assess stroke related health status. 5. Applying the Rasch method: Evaluation of the Stroke Impact Scale using Rasch Analyses The third study, the “Evaluation of the Stroke Impact Scale using Rasch Analyses” undertakes the psychometric evaluation of the Stroke Impact Scale 2.0 (SIS), in a German sample adopting Rasch based techniques. The specific aims of the study were to examine (1) the unidimensionality of the SIS domains and item fit, (2) the structure of the response scales, (3) the targeting of the domains, (4) reliability, (5) differential item functioning (DIF) or item bias for relevant patient groups, and (6) to compare the fit results of this study with the Rasch analysis results of the SIS 2.0 in a North American sample which led to the creation of the most current version of the SIS, the SIS 3.0. The Rasch analyses based on Master’s Partial Credit model has been carried out using data collected from stroke patients in Germany within an ongoing multicentric international study. 196 stroke patients from 16 study centers participated in the study and completed the Stroke Impact Scale. Unidimensionality of the eight SIS domains was confirmed according to the mean infit statistics (.97 to 1.02). 7 items displayed model misfit. Response categories of 25 items showed threshold disordering. For the domains Communication and Memory/Thinking ceiling effects (>3 logits) became apparent. Reliability values lay above .80 in six domains. No DIF was found as to age, gender, disability severity, and rehabilitation setting. Item fit results in the current study differed from those in the reference study of the SIS 2.0 in a North American sample. The SIS is according to its psychometric qualities a sufficiently robust, valid and reliable measure of stroke-specific quality of life. It seems suitable to capture consequences of stroke in patients’ with different levels of disability severity, within an inpatient as well as an outpatient setting, across age groups and genders. However, the response categories currently used with the SIS should be object to further study and revision. The fit results of the reference study of the SIS 2.0 could not be replicated and therefore, an item reduced version of the German SIS equivalent to the most current SIS 3.0 can not be created. Thus, the SIS needs to prove its cross-cultural validity in future. 6. Discussion: Towards a unified measurement approach in stroke Two complementary principles towards the description of disability have been introduced: the health status measurement and the classification approach. Connected to these conceptual approaches two methodological procedures have been regarded: the linking method and the Rasch method. The application of both methods has been illustrated. The connection of the classification approach with the health status measurement approach entails advantages reaching beyond the applications presented here. Rasch analysis and the linking method, representing qualitative and quantitative methods, may shed light on different facets of stroke measurement, which combined increase information value and lead to a complete picture of functioning and health. Advances of the classification approach, like the development of the ICF Core Sets for Stroke, and advances in health status measurement, like the application of Rasch analyses can be concatenated by the linking method. From this concatenation of different conceptual and methodological approaches, unified and comparable, conceptually sound, high quality measurement of functioning can emerge. The integration of a common reference framework with the merits of objective measurement within the proceedings of item banking and adaptive testing can contribute to compass a common standard and agreement on what and how to measure. A unified measurement approach could thereby be achieved in stroke. Advanced measurement can serve to promote precise, comprehensive, and efficient knowledge of stroke disability at the individual and at population levels, to enable better decisions for treatment and action, in the long run improving stroke care and relieving the burden to the patients.