Table 2.
Relationship between serious infection risk and oral glucocorticoid exposure for the 10 conventional models and the best fitting cumulative weighted dose model
| Model | Among cases (% or mean)* | Among controls (% or mean)* | OR (95% CI)† | OR for 5 mg increase (95% CI) | AIC‡ | AIC–AIC of the WCD model |
|---|---|---|---|---|---|---|
| Binary conventional models | ||||||
| (1) Current use | 42.1% | 24.7% | 1.84 (1.64 to 2.06) | - | 6175.0 | 115.2 |
| (2) Any use past 30 days | 52.9% | 31.1% | 2.08 (1.86 to 2.33) | - | 6122.1 | 62.3 |
| (3) Any use past 90 days | 58.6% | 34.7% | 2.26 (2.02 to 2.54) | - | 6083.6 | 23.8 |
| (4) Ever use | 74.4% | 58.5% | 1.72 (1.53 to 1.94) | - | 6201.5 | 141.7 |
| Dose-specific conventional models | ||||||
| (5) Current dosea | 11.0 mg PEQ | 7.8 mg PEQ | 1.04 (1.04 to 1.05) | 1.24 (1.19 to 1.30) | 6171.3 | 111.4 |
| (6) Average dose in past 30 daysb | 8.3 mg PEQ | 6.2 mg PEQ | 1.07 (1.06 to 1.08) | 1.41 (1.33 to 1.49) | 6124.0 | 64.2 |
| (7) Average dose in past 90 daysb | 7.1 mg PEQ | 5.4 mg PEQ | 1.09 (1.08 to 1.11) | 1.56 (1.46 to 1.67) | 6094.8 | 34.9 |
| (8) Average dose since study entryb | 5.4 mg PEQ | 3.7 mg PEQ | 1.08 (1.06 to 1.09) | 1.45 (1.35 to 1.56) | 6166.6 | 106.8 |
| (9) Peak dose in past 30 daysc | 13.6 mg PEQ | 9.3 mg PEQ | 1.03 (1.02 to 1.03) | 1.14 (1.10 to 1.17) | 6187.3 | 127.5 |
| (10) Peak dose in past 90 daysc | 15.2 mg PEQ | 10.9 mg PEQ | 1.02 (1.01 to 1.02) | 1.10 (1.07 to 1.12) | 6200.3 | 140.5 |
| Flexible model incorporating weighting by recency of treatment | ||||||
| (11) Final WCD (3-year with 3 degrees of freedom) | § | § | § | § | 6059.8 | 0 (minimum AIC) |
OR, adjusted for all a priori confounders.
For models representing exposure by binary indicator variables (1–4), the value provided is the proportion of cases/controls with the defined glucocorticoid exposure. For models with continuous exposure (5–10), the mean value of the exposure variable among glucocorticoid therapy users for cases/controls is given (seea–c below).
For dose-specific models (5–10), OR represents risk per 1 mg PEQ increase.
A lower AIC value indicates a better fit to data.
Because the (non-parametric) WCD model estimates exposure effect using flexible spline functions, the estimated effect cannot be summarised by a single parameter. See figure 1 for the estimated weight function and table 3 for the WCD model estimates of adjusted OR associated with selected exposure patterns.
Mean current dose=mean dose in current users.
Average dose in past 30/90 days/since study entry=average dose over the past 30/90 days/since study entry in subjects who used glucocorticoid therapy for at least 1 day in past 30/90 days since study entry.
Mean peak dose in past 30/90 days=mean peak dose in past 30/90 days in subjects who used glucocorticoid therapy for at least 1 day in past 30/90 days.
AIC, Akaike information criterion; PEQ, prednisolone equivalent; WCD, weighted cumulative dose.