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- SUBJECTS AND METHODS
The use of an overall health status measure, particularly self-rated health (SRH), in population and clinical health surveys has become common (1–4). Historically, much of the work on SRH has focused on its predictive ability for a range of health outcomes, including social-psychological wellbeing (5–7), morbidity (8–10), health care utilization (10–12), and mortality (10, 13, 14). More recently, interest in understanding the determinants of SRH has increased. Predictors of good SRH include younger age (15–17), male sex (15), higher socioeconomic status (15, 16, 18), social support (19, 20), and absence of chronic conditions and pain (15–17, 21–23). Although physiologic and psychological determinants of good SRH have been documented, the main determinant appears to be physical health (15, 24, 25).
The most significant predictor of poor SRH is the presence of chronic conditions (15, 17, 21, 22, 26). However, population-based and clinical studies indicate that 30–80% of persons with at least 1 chronic condition report good health (15–17). This raises questions about the distinction between individuals' perceptions of their health status and a diagnosed medical condition. It has been suggested that some individuals think about specific health problems when asked to rate their health, whereas others think in terms of general physical functioning or health behaviors (27). Pain is a common reason for seeking medical care around the world (28–30), and is associated with poor SRH (15–17, 23). Studies indicate that chronic pain seems to relate to poor health more strongly than chronic diseases or age, and the significant association persists even when sociodemographic and relevant health factors are considered (16, 17).One possible explanation is that pain is a mediator between chronic conditions and SRH. This study explores this idea by examining the onset of arthritis.
All forms of arthritis share the common symptom of pain and have a major impact on functioning and health care utilization (31–38). Concern about arthritis as a public health problem is growing in North America (39), with large projected increases in prevalence as the population ages (37, 40). The population impact of arthritis has been well documented in the literature. The most frequent symptoms reported by adult men and women are pains in the musculoskeletal system (23), and arthritis is the most common cause of disabilities and activity limitations (35, 41). Having arthritis has consistently been shown to be associated with poor SRH (4, 22, 23, 37, 42, 43). Functional limitations associated with musculoskeletal conditions have also been associated with poorer health status (21–23, 42, 43). Previous cross-sectional studies examining the independent effects of several conditions have shown arthritis, and musculoskeletal symptoms generally, to be among the conditions with the strongest associations with reporting poor SRH (23, 42).
Studies examining the determinants of SRH have been predominantly cross-sectional. Few studies have examined predictors of change in SRH, and even fewer have examined the relevance of changes in factors associated with SRH to predicting changes in SRH. This study explores the potential role of worsening pain and development of activity limitation as hypothesized mediators in the relationship between the onset of arthritis and worsening SRH over time by examining data collected from a Canadian cohort over a 2-year period. Given the impact of chronic conditions on SRH generally, the onset of other chronic conditions are considered.
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- SUBJECTS AND METHODS
The prevalence of characteristics of interest at baseline are presented in Table 1. Approximately 10% of respondents reported their health as being fair/poor, ∼15% reported some level of pain, and 17% reported the presence of arthritis. Almost 50% reported at least 1 nondisabling condition, and ∼20% reported at least 1 disabling condition. At followup, a greater proportion of individuals reporting worse SRH were older, of lower income, and lower education levels than those without worse SRH (Table 2).
Table 1. Prevalence of selected characteristics in the Canadian population at baseline, 1998/2000 Canadian longitudinal National Population Health Survey*
|Variable||Prevalence at baseline|
|Self-rated health|| |
| Fair/poor||9.1 (8.34–9.88)|
| Good||26.7 (25.55–27.84)|
| Excellent/very good||64.2 (62.98–65.42)|
|Usual intensity of pain/ discomfort|| |
| No pain||85.8 (85.02–86.65)|
| Mild||4.4 (3.88–4.92)|
| Moderate||8.1 (7.42–8.73)|
| Severe||1.7 (1.42–1.96)|
|With activity limitation||18.9 (17.90–19.98)|
|With arthritis||17.0 (16.18–17.8)|
|≥ 1 non-disabling condition||47.2 (45.91–48.43)|
|≥ 1 disabling condition||19.0 (18.00–20.06)|
|≥ 1 life-threatening condition||9.0 (8.30–9.67)|
Table 2. Percentage distribution of self-rated health (SRH) status by sociodemographic characteristics in the Canadian population using data from the 1998/2000 Canadian longitudinal National Population Health Survey
|Variable||Worse SRH||No worse SRH|
|Age, years|| || |
|Sex|| || |
|Income adequacy|| || |
|Education level|| || |
| Less than secondary||26.3||20.1|
| Some post-secondary||28.6||28.7|
Almost 6% of the population reported developing arthritis, 20% reported worse SRH, ∼9% reported worse pain, and 7% developed an activity limitation. Other new chronic conditions were reported by 5–23% of respondents, with the greatest change being new nondisabling conditions. The proportions of respondents who developed each of the followup outcomes who also reported developing other outcomes are presented in Table 3. For example, almost 30% of individuals who developed arthritis reported worse SRH and 25% reported worse pain.
Table 3. Percentage of people who developed specified outcomes, and also reported developing additional outcomes, from the 1998/2000 Canadian longitudinal National Population Health Survey*
|Developed outcomes||Overall||% with developed outcomes who developed additional outcomes|
|Arthritis||Worse SRH||Worse pain||Activity limitation||Non-disabling condition||Disabling condition||Life-threatening condition|
Results from the main effects models indicate that a significant relationship exists between arthritis onset and worse pain, developing an activity limitation, and worse SRH at followup (Table 4, Figure 1B). Respondents who reported developing arthritis were 30% more likely to report worse SRH and 3 times as likely to report worse pain, compared with those who did not develop arthritis. The development of new chronic conditions also had a substantial and independent effect on developing each of these outcomes. With each new life-threatening condition, the odds of reporting worse SRH more than doubled, and with the development of each new disabling condition, the odds of worse pain and new activity limitation more than doubled.
Table 4. Results from the main effects models for reporting specified outcome at followup, 1998/2000 Canadian longitudinal National Population Health Survey*
|Variable of interest†||Model outcomes|
|Model 1 worse pain||Model 2 activity limitation||Model 3 worse SRH|
|New arthritis||3.09 (2.202–4.322)||1.70 (1.176–2.420)||1.30 (1.002–1.683)|
|New non-disabling condition||1.27 (1.097–1.467)||1.45 (1.231–1.697)||1.19 (1.072–1.325)|
|New disabling condition||2.23 (1.783–2.786)||2.35 (1.852–2.981)||1.52 (1.289–1.784)|
|New life-threatening condition||1.51 (1.101–2.084)||1.89 (1.355–2.638)||2.35 (1.865–2.961)|
The findings from the mediated models are illustrated in Table 5 and Figure 1C. With the introduction of worse pain into the model, arthritis onset no longer had a statistically significant association with worsening SRH. This is indicative of a mediating effect via worsening pain (Table 6). The relationship between arthritis onset and developing an activity limitation also became nonsignificant with the introduction of worse pain into the model, where a 55% decrease in effect was observed (Table 6). Again, this suggests that pain is a significant mediator of this relationship. A total decrease of almost 60% in arthritis-onset effect on worsening SRH was observed when both mediating factors were considered (Table 6). Although worsening pain and developing an activity limitation had independent associations with worsening SRH, the effect of worsening pain was diminished by 20% when developing an activity limitation was considered. This suggests a partially mediated effect via development of an activity limitation for worsening pain.
Table 5. Results from the mediated models for reporting specified outcome at followup, 1998/2000 Canadian longitudinal National Population Health Survey*
|Variable of interest†||Model outcomes|
|Model 4 worse SRH||Model 5 activity limitation||Model 6 worse SRH|
|New arthritis||1.16 (0.886–1.509)||1.31 (0.922–1.875)||1.13 (0.865—1.485)|
|Worse pain||2.15 (1.760–2.636)||4.24 (3.308–5.437)||1.90 (1.549–2.324)|
|Developed an activity limitation||–||–||2.20 (1.797–2.693)|
|New non-disabling condition||1.17 (1.050–1.303)||1.41 (1.185–1.668)||1.14 (1.024–1.275)|
|New disabling condition||1.41 (1.197–1.659)||2.06 (1.610–2.637)||1.33 (1.129–1.565)|
|New life-threatening condition||2.27 (1.794–2.870)||1.74 (1.238–2.458)||2.17 (1.730–2.732)|
Table 6. Percentage of decrease in the effect of conditions on outcomes having accounted for worse pain and/or new activity limitation, 1998/2000 Canadian longitudinal National Population Health Survey*
|Variable of interest||Outcomes|
|NAL with variable worse pain (model 5 vs 2)||Worse SRH with variable worse pain (model 4 vs 3)||Worse SRH with variables worse pain and NAL (model 6 vs 3)||Worse SRH with variables worse pain and NAL (model 6 vs 4)|
Tables 4 and 5 also present findings for the main effects of the onset of other chronic conditions. With the introduction of worsening pain and developing an activity limitation into the models, odds ratios were slightly reduced, suggesting some mediation via these variables. However, the extent of mediation was less than with the onset of arthritis. Percentage decreases in effects are presented in Table 6.
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- SUBJECTS AND METHODS
In this analysis of longitudinal population survey data, the association between developing arthritis and worsening SRH was explained by the intermediary of worsening pain. The effect of this intermediary was partially mediated by development of an activity limitation. The very small residual direct effect of arthritis onset was not found to be significant. This is the first study to date that examines these relationships longitudinally and considers both of these hypothesized mediators. Worsening pain and developing activity limitations also explained a portion of the relationships between the onset of other chronic conditions and worsening SRH, but to a lesser extent than with arthritis onset. Pain seems to have the largest mediating effect on new disabling conditions. This may be related to the fact that back problems are the most frequent condition in this group. To some extent, the findings from this study explain why there appears to be a stronger relationship between pain and poor health status than between chronic diseases and poor health status (16, 17).
Most studies that have found a relationship between other chronic conditions and poorer self-reported health status have looked at these relationships either by examining a list of specific conditions or by considering the number of chronic conditions overall (16, 17, 23, 42, 43). This study examined chronic conditions by considering the onset frequency of broad types of conditions over the study period. Although a mediating role for pain was most evident with the onset of disabling conditions, there are likely other and differing mediators for different conditions. For example, we hypothesize that the relationship between the onset of some life-threatening conditions (such as diabetes and chronic heart disease) and SRH might be mediated by perceptions of disease seriousness in addition to the severity of actual physical symptoms. This is an area for further study.
In their studies examining the determinants of poor SRH in the elderly, including several conditions, Molarius and Janson (23) found pain and Hoeymans et al (42) found activity limitations to be significantly associated with poor SRH. Hoeymans et al documented a decreased effect of chronic conditions on poor SRH upon inclusion of activity limitations (42). In contrast, although Molarius and Janson conceptually acknowledged a role for pain, they did not report whether any change in effect of chronic conditions was observed when pain was considered (23). Also, neither study considered the effect of both pain and activity limitations.
This study has several limitations, one being that data were obtained through self report. However, it is known that the agreement between self-reported chronic conditions and medical records is fair to good, depending on the type of disease being investigated (47–49). Nonetheless, we contend that the ability or inability of medical records to corroborate a person's self report of having a condition, let alone whether they experience pain or have activity limitations, has little if any effect on how they report their own health status.
The grouping of conditions into broad categories is undoubtedly subjective. Also, any category that includes a condition(s) less severe than those remaining would inevitably bias results toward the null for the particular category. However, the significant associations with specified outcomes that we found by condition type are encouraging. As expected, we found life-threatening conditions to have the strongest association with worse SRH, and disabling conditions to have the strongest associations with worsening pain and developing an activity limitation.
Although the direction of the arrows as presented in Figure 1 is not supported by the current data and analyses, their direction is founded on theoretical and practical knowledge described earlier. Also, there is debate as to the proper method to test the statistical significance of mediation (50). Most of the work in this area has been based on continuous outcomes rather than on binary outcomes as considered in this study. However, despite the large sample size, the direct effect of arthritis onset, net of worsening pain, and development of activity limitations were found to be insignificant, leaving little doubt as to the significance of mediation.
Because poor SRH is predictive of several negative health outcomes, a better understanding of the relationship between disease and self-perceived health status is essential if target areas for prevention and intervention are sought. This study aimed to elucidate this relationship over time, particularly for developing arthritis. Worsening pain fully explained the effects of developing arthritis on worsening SRH; the effects of pain were further mediated by the development of activity limitations. This suggests that it was these symptoms rather than arthritis as such that were associated with worse SRH, at least in the short term, with implications for the clinical management of this condition. A better understanding of the nature of symptoms and other factors that mediate the effect of chronic conditions might point to important areas of intervention to reduce their impact on SRH.