Table 4.
Summary of main results
| Disease measure | Crudea ORs
|
Adjustedb ORs
|
Adjustedc ORs
|
|||
|---|---|---|---|---|---|---|
| OR (95% CI) | P-value | OR (95% CI) | P-value | OR (95% CI) | P-value | |
| Exacerbation frequency | ||||||
| Infrequent | 1 | 1 | 1 | |||
| Frequent | 1.06 (0.97, 1.15) | 0.18 | 1.06 (0.97, 1.15) | 0.22 | 1.05 (0.96, 1.14) | 0.29 |
| GOLD (FEV1) staging | ||||||
| Mild | 1 | 1 | 1 | |||
| Moderate | 1.15 (1.01, 1.30) | 0.031 | 1.17 (1.03, 1.33) | 0.013 | 1.16 (1.03, 1.32) | 0.018 |
| Severe/very severe | 1.08 (0.94, 1.23) | 0.280 | 1.16 (1.02, 1.33) | 0.030 | 1.14 (1.00, 1.31) | 0.058 |
| Medication-based staging | ||||||
| Mild/moderate | 1 | 1 | 1 | |||
| Severe | 1.16 (1.07, 1.26) | 0.001 | 1.16 (1.07, 1.27) | 0.001 | 1.17 (1.06, 1.26) | 0.001 |
| Very severe | 1.52 (1.37, 1.69) | 0.001 | 1.54 (1.38, 1.72) | <0.001 | 1.52 (1.37, 1.69) | <0.001 |
Notes:
Adjusted for age, sex, and GP practice (matching variables).
Adjusted for age, sex, GP practice, BMI, and smoking habits.
Adjusted for age, sex, GP practice, BMI, smoking habits, CVDs [composite measure], and heart failure. To avoid having a small number of subjects in the reference category and thus compromising the precision of the effect estimates, the normal weight category (as opposed to underweight) was selected as the baseline for BMI and ex-smokers (as opposed to never smoked) the baseline for the smoking status variable in all regression models. Having examined the distribution of subjects among the disease severity categories as part of the descriptive analysis, the “severe” and “very severe” categories (GOLD stage 3+4) were collapsed into one (when disease is staged by spirometry, less than 10% of patients are categorized as having very severe disease). Likewise, in the case of the alternative, proxy measure of disease severity based on COPD medication history, the categories “mild” and “moderate” were collapsed into a single category (this then becomes the reference category).
Abbreviations: BMI, body mass index; CI, confidence interval; CVD, cardiovascular disease; FEV1, forced expired volume in 1 second; GOLD, Global Initiative for Chronic Obstructive Lung Disease; GP, general practitioner; OR, odds ratio.