Table 3. Summary of the main findings for each imputation method in data missing at random.
| Method | Performance measure* | ASDAS | ASDAS<2.1 | ||||
| Baseline | 6 months | 12 months | Baseline | 6 months | 12 months | ||
| Unconditional M-SI | Bias | Strong over-estimation | Slight under-estimation | Slight under-estimation | Strong under-estimation | Strong over-estimation | Strong over-estimation |
| Conditional M-SI | Bias | – | Slight under-estimation | – | – | Moderate over-estimation | – |
| Deterministic LR-SI | Bias | Moderate under-estimation | Close to unbiased | Slight over-estimation | Moderate under-estimation | Moderate over-estimation | Moderate over-estimation |
| Random LR-SI | Bias | Moderate under-estimation | Close to unbiased | Slight over-estimation | Strong over-estimation | Moderate under-estimation | Moderate under-estimation |
| Unconditional HD-SI | Bias | Strong over-estimation | Slight under-estimation | Slight under-estimation | Strong under-estimation | Slight over-estimation | Moderate over-estimation |
| Conditional HD-SI | Bias | – | – | – | – | – | – |
| Predictive mean deterministic HD-SI | Bias | Slight under-estimation | Close to unbiased | Close to unbiased | Strong over-estimation | Slight over-estimation | Close to unbiased |
| Predictive mean random HD-SI | Bias | Slight under-estimation | Close to unbiased | Close to unbiased | Strong over-estimation | Slight over-estimation | Slight over-estimation |
| Weighted predictive mean random HD-SI | Bias | Close to unbiased | Close to unbiased | Slight under-estimation | Strong over-estimation | Close to unbiased | Slight over-estimation |
| Random LR-MI | Bias | Moderate under-estimation | Close to unbiased | Slight over-estimation | Strong over-estimation | Moderate under-estimation | Moderate under-estimation |
| Coverage | Strong under-coverage | Slight under-coverage | Slight under-coverage | Strong under-coverage | Moderate under-coverage | Moderate under-coverage | |
| Unconditional HD-MI | Bias | Strong over-estimation | Slight under-estimation | Slight under-estimation | Strong under-estimation | Slight over-estimation | Moderate over-estimation |
| Coverage | Strong under-coverage | Slight under-coverage | Strong under-coverage | Strong under-coverage | Slight under-coverage | Strong under-coverage | |
| Conditional HD-MI | Bias | – | – | – | – | – | – |
| Coverage | – | – | – | – | – | – | |
| Predictive mean random HD-MI | Bias | Slight under-estimation | Slight under-estimation | Close to unbiased | Strong over-estimation | Slight over-estimation | Slight over-estimation |
| Coverage | Strong under-coverage | Slight under-coverage | Moderate under-coverage | Strong under-coverage | Slight under-coverage | Moderate under-coverage | |
| Weighted predictive mean random HD-MI | Bias | Close to unbiased | Close to unbiased | Slight under-estimation | Moderate over-estimation | Slight over-estimation | Slight over-estimation |
| Coverage | Moderate under-coverage | Slight under-coverage | Slight under-coverage | Moderate under-coverage | Slight under-coverage | Moderate under-coverage | |
‘–’ indicates that results were not produced due to insufficient number of individuals in classes in the simulated datasets.
Assessment of bias: close to unbiased (<1%), slight bias (1%–5%), moderate bias (5%–10%) and strong bias (>10%). Assessment of coverage: correct coverage (Monte Carlo 95% CIs of coverage include 95%), slight under-coverage (90%–95%), moderate under-coverage (80%–90%), strong under-coverage (<80%) and over-coverage (95%–100%). Monte Carlo 95% CIs of coverage were calculated based on corresponding 1.96 Monte Carlo SEs.
Strong under-coverage was observed for all single imputation methods.
ASDASAxial Spondyloarthritis Disease Activity ScoreHD-MIhot deck multiple imputationHD-SIhot deck single imputationLR-MIlinear regression multiple imputationLR-SIlinear regression single imputationM-SImean single imputation