Previous estimates of individual and population attributable risksi for adverse outcomes due to chronic conditions have considered only a limited number of conditions and outcomes, with some studies using inappropriate formulae or methods of estimation. This study re-examines the magnitude of individual and population attributable risks for a wide range of conditions and various health outcomes.
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Log-Poisson regression was used to calculate prevalence ratios as an indicator of individual risk and population-associated fractionsii of 13 chronic conditions, examining activity limitations, self-rated health and physician visits. The effect of multimorbidity on prevalence ratios was examined.
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Canada, 2000-01.
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Nationally representative sample of Canadians aged 12+ years (n = 130 880).
At the individual level, fibromyalgia/chronic fatigue syndrome and cancer, and to a lesser extent stroke and heart disease, were associated with an increased risk of both activity limitations and a self-rated health status of fair or poor; high blood pressure was associated with four or more physician visits in the previous 12 months. In contrast, population attributable fractions were substantial for arthritis/rheumatism, heart disease, back problems and high blood pressure across all outcomes. Adjustment for multimorbidity resulted in a marked decrease in prevalence ratios. See Tables and interpretations in the next section.
Differences in the ranking of individual risks and population attributable fractions for different diseases and outcomes are substantial. This needs to be taken into account when setting priorities, as interventions may need to be targeted to different conditions depending on which aspects of health are being considered, and whether the focus is on individuals, such as in clinical care, or improving the health of the population.
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| Prevalence (%) of study outcomes, overall and by chronic condition | |||||
|---|---|---|---|---|---|
| Population prevalence of conditions (%) | Activity limitations | Fair/poor Self-Rated Health | Four or more F/GP visits | ||
| Population prevalence | 11.6 | 12 | 28.5 | ||
| Chronic condition (by order of overall prevalence) | |||||
| Allergies | 28.5 | 15.5 | 13.8 | 34.7 | |
| Back problems | 17.5 | 18.9 | 23.5 | 43.6 | |
| Arthritis/rheumatism | 15.2 | 29.2 | 31.8 | 51.5 | |
| High blood pressure | 12.6 | 24.3 | 31.2 | 56.4 | |
| Migraines | 9.1 | 19.7 | 20.2 | 45.5 | |
| Asthma | 8.4 | 23.8 | 20.7 | 43.6 | |
| Heart disease | 5 | 39.8 | 49 | 63.3 | |
| Thyroid condition | 4.8 | 24.6 | 23.5 | 48.7 | |
| Crohn's disease/colitis/ulcers | 4.7 | 28.8 | 34.2 | 54.7 | |
| Diabetes | 4.1 | 31.8 | 42.6 | 61.1 | |
| Cancer | 1.7 | 41.2 | 47.3 | 60 | |
| Fibromyalgia/chronic fatigue syndrome | 1.6 | 49.3 | 52.2 | 67.1 | |
| Suffering from effects of stroke | 1 | 55.3 | 63.2 | 67.7 | |
Note: F/GP visits: Family/General Practitioner visits.
This table presents the population prevalence of chronic conditions and study outcomes. The four most common conditions were allergies (28.5%), back problems (17.5%), arthritis/rheumatism (15.2%), and high blood pressure (12.6%). Twelve percent of individuals reported their health status as fair/poor and a similar proportion reported having some activity limitation. Table 1 also presents the proportion of individuals within each condition group who reported the outcomes. Generally, it is the less frequent conditions that tend to be more “severe,” in that a higher proportion of the population reports an adverse outcome. The pattern of association of conditions is different for different outcomes.
| Prevalence (%) in people with activity limitations | PR unadjustediii for multimorbidity | PR adjustediv for multimorbidity | PAF (%) | ||
|---|---|---|---|---|---|
| Age (years) (ref: 12-19 years) | |||||
| 20-29 | 0.90 (0.80 to 1.00) | ||||
| 30-39 | 0.99 (0.90 to 1.10) | ||||
| 40-49 | 1.27* (1.16 to 1.40) | ||||
| 50-59 | 1.48* (1.34 to 1.63) | ||||
| 60-69 | 1.66* (1.50 to 1.83) | ||||
| 70-79 | 1.67* (1.51 to 1.85) | ||||
| 80+ | 1.65* (1.46 to 1.87) | ||||
| Gender (ref: male) | |||||
| Female | 1.20* (1.15 to 1.25) | ||||
| Chronic condition | |||||
| Allergies | 38.1 | 1.63* (1.56 to 1.70) | 1.22* (1.17 to 1.28) | 6.9 | |
| Back problems | 28.6 | 1.68* (1.61 to 1.76) | 1.18* (1.12 to 1.24) | 4.3 | |
| Arthritis/rheumatism | 38.3 | 2.42* (2.31 to 2.55) | 1.78* (1.69 to 1.88) | 16.8 | |
| High blood pressure | 26.4 | 1.58* (1.51 to 1.67) | 1.22* (1.15 to 1.28) | 4.7 | |
| Migraines | 15.5 | 1.93* (1.82 to 2.04) | 1.36* (1.28 to 1.45) | 4.1 | |
| Asthma | 17.3 | 2.40* (2.28 to 2.53) | 1.76* (1.66 to 1.87) | 7.5 | |
| Heart disease | 17.1 | 2.62* (2.49 to 2.77) | 1.78* (1.68 to 1.89) | 7.5 | |
| Thyroid condition | 10.1 | 1.48* (1.38 to 1.58) | 1.18* (1.10 to 1.27) | 1.5 | |
| Crohn’s disease/colitis/ulcers | 11.7 | 2.21* (2.09 to 2.34) | 1.35* (1.27 to 1.45) | 3.1 | |
| Diabetes | 11.3 | 2.00* (1.88 to 2.12) | 1.49* (1.40 to 1.60) | 3.7 | |
| Cancer | 6.2 | 2.40* (2.22 to 2.58) | 1.93* (1.78 to 2.11) | 3.0 | |
| Fibromyalgia/chronic fatigue syndrome | 6.9 | 3.59* (3.34 to 3.85) | 2.02* (1.84 to 2.22) | 3.5 | |
| Stroke | 4.8 | 2.96* (2.72 to 3.21) | 1.87* (1.68 to 2.08) | 2.3 | |
Table 2 presents the prevalence of chronic conditions among the outcome groups activity limitations; fair/poor SRH and 4+ F/GP consultations, respectively, and the association between the conditions and outcomes, presented as prevalence ratios (PRs) both unadjusted and adjusted for multimorbidity. All estimates are adjusted for age and gender. The importance of taking multimorbidity into account is illustrated by the difference between unadjusted PRs and adjusted PRs. Adjusted population-associated fractions (PAF), estimated using adjusted-prevalence ratios, indicated that, in the case of activity limitations and fair/poor self-reported health, arthritis/rheumatism overwhelmingly had the greatest population-level impact, at 17% and 16% respectively. The conditions with the second greatest impact were asthma and heart disease at 8% each. In the case of fair/poor self-rated health, arthritis/rheumatism was followed by back problems (12%) and high blood pressure (11%). For 4+ family/general practitioner consultations, PAFs were greatest for high blood pressure (9%), followed by back problems (7%) and arthritis/rheumatism (6%).
The following three figures show the prevalence of activity limitations, poor self-rated health, and GP visits by chronic condition.
Note: PR= population prevalence; AL= allergies; BK= back problems; A/R=arthritis/rheumatism; HBP=high blood pressure; MG=migraine; AS=asthma; HD=heart disease; TH=thyroid; GI=gastrointestinal; DB=diabetes; CA=cancer; F/CFS=Fibromyalgia/Chronic fatigue syndrome; SK=stroke.
The following three figures present the population associated fractions for activity limitations, poor self-rated health, and GP visits by chronic condition.
