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- APPENDIX A
Osteoarthritis (OA) affects an estimated 25% of the general population aged 55 years and older (1). It is one of the most common chronic health conditions in this age group and, in light of projected demographic trends, the total number of people with the disease is likely to increase (2). An important question is how to measure the impact of OA on individuals and society.
Population-based epidemiologic studies of OA have consistently highlighted discrepancies between radiographic evidence of joint pathology on the one hand and patient reports of pain severity and levels of disability on the other (3–5). Such discordance has been reported in other conditions as well (6–8). It suggests that the level of suffering and the impact on everyday life among individuals with joint pain and OA may be highly variable, even when the severity of the underlying disease pathology is comparable.
The recently revised International Classification of Impairment, Disability, and Handicap (ICIDH)—now referred to as the International Classification of Functioning, Disability and Health (ICF) (9)—offers a useful framework with which to describe the various consequences of OA. The ICF classifies functioning at 3 distinct levels: anatomic/physiologic (body function), individual person (activities), and societal (participation). Abnormal functioning at the 3 levels is described, respectively, as impairment (e.g., pain, stiffness), activity limitation (e.g., difficulty walking 100 yards), and participation restriction (e.g., difficulty looking after others). They broadly correspond to the older typology of impairment, disability, and handicap. A range of contextual factors in an individual's life, both personal and environmental, may act upon function at each level and modify relationships between these different levels (please refer to Appendix for definitions of terms).
Previous epidemiologic studies of OA have investigated the prevalence of impairment (e.g., radiographic joint space narrowing and osteophytes). However, there is increasing interest in the societal and personal consequences of OA (10), accompanied by a recognition that these cannot be inferred from levels of impairment or activity limitation alone (11). For example, Heberdens nodes may not affect functional abilities of the hand, but may result in social isolation due to feelings of inadequacy resulting from observable deformity. Hence, directly measuring levels of participation and participation restriction is an important step for epidemiologic research. However, the extent to which this has been satisfied in previous studies is unclear. The ICF framework is relatively new and postdates many of the epidemiologic studies in this field. Measurement of disability has been a feature of some studies (12–16) but coverage of participation restriction by the instruments used is uncertain.
As a preliminary step to investigating the prevalence, patterns, and determinants of participation restriction in population-based studies of joint pain and OA, we undertook a review of current self-report health instruments potentially relevant to the measurement of participation restriction. However, we wanted to identify instruments that could be completed by all older adults, not only those with joint pain. Our aims therefore were to 1) identify health measurement instruments that might include some measurement of participation (or participation restriction) and could be applied in a population survey; 2) reliably determine the proportion of items within these health measurement instruments that captured some aspect of participation (or participation restriction) to indicate the ability of instruments and their scores to exclusively represent participation; and 3) ascertain whether different observers with varying levels of survey experience and knowledge of the ICF framework could consistently identify participation items in these instruments.
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- APPENDIX A
We have reasoned that measuring participation in population-based studies is important for describing the personal and social consequences of joint pain in older adults. In this study, we sought to determine the extent to which existing health measurement instruments might be used in a population survey to measure levels of participation associated with joint pain. We identified a number of instruments that, by design, had the potential to be applied in this way. We rated individual items to determine the proportion within each instrument that captured participation and used this to indicate the extent to which instruments and their scale scores exclusively represent participation. Our findings demonstrate that participation coverage within these measures is variable, and there were no instruments that consisted entirely of participation items. Instruments with high proportions of relevant items may give reasonable estimates of participation frequency. However, these instruments were not designed to capture participation and contain items that do not measure participation. The removal of items that do not capture participation may affect the validity of these instruments, and further validation studies would be required prior to any application as participation measures in the population.
Instruments designed to capture societal consequences, consistent with the handicap concept, contained the greatest proportion of participation items. This was expected, as the conceptual models of handicap and participation are similar. The conceptual basis is important to consider when selecting an instrument because the underlying theory is shaping the measurement (43). Instruments designed to measure generic health status, quality of life, or the consequences of musculoskeletal conditions contained a smaller proportion of participation items. These instruments were not designed specifically to reflect the conceptual models of handicap or participation, and their ability to measure them has been questioned (44, 45).
The Reintegration to Normal Living Index contained the greatest proportion of participation items (9 of 11). It was designed as a clinical tool to measure levels of global function and has been applied in survey questionnaires (37, 46). The second highest proportion was in the Impact on Participation and Autonomy (15 of 23), designed as a handicap questionnaire (38). Both questionnaires contained items that were not rated as participation items. This may reflect differences between the concepts of participation and handicap. Measurement of handicap has proven challenging, with the small number of instruments and lack of uniformity between them suggesting the concept is underdeveloped (34, 45). It remains to be seen if similar problems occur with participation.
Our findings were based on an analysis of instruments that might contain participation items. These were identified by a comprehensive and reproducible search of published literature and application of standard criteria to include only those that could be applied in population surveys to measure participation in relation to joint pain. We know of no other instruments for inclusion. Those such as the Western Ontario McMaster Universities Osteoarthritis Index (47), the Roland and Morris Low Back Questionnaire (48), and the Disabilities of the Arm, Shoulder and Hand outcome measure (49) were not included because they were designed to capture consequences of site-specific conditions. The WHO Disability Assessment Schedule (50) was published after our searches were performed. Other instruments with participation items (e.g., Assessment of Life Habits ) were not designed to be self completed.
In the absence of a gold standard, we used agreement between the experienced assessors to determine the proportion of items within each instrument that captured participation. There are no other studies with which to compare this level of agreement. However, the level of agreement beyond chance for the experienced assessors was significantly higher than for the inexperienced assessors. Intra-assessor variation was not assessed. We cannot therefore conclude whether the disagreement within the inexperienced pair or within the experienced pair was reflecting general inconsistencies or systematic differences. However, agreement beyond chance between the inexperienced assessors was poor compared with that achieved by the experienced pair. This suggests that greater experience and familiarization with the WHO concepts lead to a greater common understanding and certainty in the application of these concepts.
To guide the development of the conceptual and measurement models of participation, the main sources of disagreement were analyzed. Assessors found it difficult to determine if actions, tasks, or life situations occurred at the level of the individual (i.e., activities) or society (i.e., participation), an issue that also affected the application of the ICIDH (52). For example, with the item “Are you able to use the telephone?” (Self-Evaluation of Life Function question 3 ), one assessor from each pair assessed the item as measuring participation, whereas the other assessor did not. Disagreement concerned whether the telephone is a contextual factor that affects the fulfillment of the task.
There were 97 items that the experienced and the inexperienced observers agreed captured participation, and these provide examples of participation items likely to be recognized more straightforwardly by any observer. Such items did not refer to specific actions, tasks, or life situations, but captured a collection of them, similar to the domain and subdomain headings presented in the ICF. For example, “I participate in social activities with family, friends, and/or business acquaintances as is necessary or desirable to me” (Reintegration to Normal Living Index question 7 ).
The level of disagreement between the inexperienced assessors raises questions about the ability of the participation concept to be quickly understood and easily applied. It suggests that WHO literature does not lead to a consistent understanding of the concept, which may be why it is measured in a number of ways. The WHO, in introducing the ICF, does not present a gold standard for measurement or specific strategies of measurement, but instead present a base that requires tailoring to meet specific needs (53) as well as a description of the concept (54). To apply the concept for research purposes, further development and direction is required.
In conclusion, there appear to be no existing health measurement instruments consisting entirely of participation items. It may be appropriate to develop both the concept and its translation into measurement to capture levels of participation in the general population.