Table 2.
Comparison of Nine Methods with and without Adjustment for Covariates
| Unit of Analysis | Method of Analysis | Unadjusted for Covariates | Adjusted for Covariates | ||
|---|---|---|---|---|---|
| OR | 95% CI | OR | 95% CI | ||
| Cluster | Un-weighted Regression | 1.05 | (0.59 1.87) | 1.05 | (0.60 1.84) |
| Weighted Regression | 1.27 | (0.81 1.99) | 1.27 | (0.82 1.96) | |
| Random-effects Meta Regression | 1.05 | (0.60 1.85) | 1.05 | (0.61 1.82) | |
| Individual | Standard Logistic Regression | 1.14 | (0.93 1.39) | 1.17 | (0.95 1.44) |
| Robust Standard Error | 1.14 | (0.72 1.80) | 1.17 | (0.79 1.73) | |
| Generalized Estimating Equations ** | 1.14 | (0.72 1.80) | 1.15 | (0.76 1.72) | |
| Modified GEE (1) *** | 1.14 | (0.71 1.83) | |||
| Modified GEE (2) **** | 1.14 | (0.71 1.84) | |||
| Random-effects Meta Analysis | 1.09 | (0.68 1.74) | 1.12 | (0.73 1.70) | |
| Random-effects Logistic Regression | 1.10 | (0.65 1.86) | 1.13 | (0.71 1.80) | |
| Bayesian Random-effects Regression | 1.12 | (0.64 1.95) | 1.13 | (0.68 1.87) | |
OR = odds ratio; CI = confidence interval
* For the cluster level analysis, include 'center' (i.e. Hamilton and Ottawa) as the covariate; for the individual level analysis, include 'diabetes at baseline', 'heart disease at baseline', and 'BP controlled at baseline' as the covariates.
** The intra-cluster correlation coefficient (ICC) estimated from GEE are 0.077 and 0.054 when unadjusted for covariates and adjusted for covariates respectively.
*** The confidence interval was calculated based on the corrected standard error which was equal to the sandwich standard error estimator multiply by 
, where J is the number of clusters in each arm.
**** The Confidence interval was calculated based on the quantiles from the t-distribution with 2(J-1) degrees of freedom instead of quantiles from the standard normal distribution.