Table 3.
Estimates of Association Between β-Interferon Treatment and Time to a Sustained EDSS Score of 6, Obtained Using Different Analytical Approaches, Among Multiple Sclerosis Patients From British Columbia, Canada, 1995–2008
| Type of Adjustment, by Model Type | Measure of Association | 95% CI |
|---|---|---|
| Cox | ||
| Unweighteda | 1.29b | 0.91, 1.82c |
| Weighted by sw(n) | 1.36b | 0.95, 1.94d |
| Pooled logistic | ||
| Unweighteda | 1.29e | 0.91, 1.82c |
| Weighted by sw(n) | 1.36e | 0.96, 1.95d |
| Poisson | ||
| Weighted by sw(n) | 1.36e | 0.96, 1.95d |
| Complementary log-log | ||
| Weighted by sw(n) | 1.37e | 0.96, 1.95d |
Abbreviations: CI, confidence interval; EDSS, Expanded Disability Status Scale.
a Based on time-dependent β-interferon treatment exposure status and covariates measured at baseline: EDSS score, age, disease duration, and sex. This estimate does not have a causal interpretation and is shown for comparison purposes.
b The hazard ratio is the measure of association obtained from a Cox model.
c 95% CIs were calculated based on robust standard errors.
d 95% CIs were obtained from 500 nonparametric bootstrap samples.
e The hazard ratio from the Cox model was approximated by the odds ratio from the pooled logistic model (49, 50) (see Web Appendix 3) or, under the infrequent event assumption, by the standardized mortality ratio from Poisson regression or by the odds ratio from complementary log-log regression, respectively. The weighted Cox model (19, 22) was approximated using weighted versions of these models. Software specifications for these analyses are provided in Web Appendix 5.