Table 3.
Overview of cost estimates for the missing data methods
| RA | CCA (% bias) | MI-PMM (% bias) | Log MI-PMM (% bias) | Two-step MI (% bias) | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| M | M + H | M | M + H | M | M + H | M | M + H | M | M + H | |
| 17 % Missing data | ||||||||||
| n | 237 | 193 | 201 | 154 | 237 | 193 | 237 | 193 | 237 | 193 |
| Mean cost (euros) | 50,560 | 37,767 | 53,148 | 38,933 | 51,369 | 37,935 | 51,966 | 38,137 | 52,685 | 38,482 |
| SE mean (euros) | 5359 | 3063 | 6056 | 3744 | 5650 | 3268 | 5652 | 3309 | 5642 | 3394 |
| Treatment cost difference (euros) | −12,792 | −14,215 (11) | −13,434 (5) | −13,829 (8) | −13,203 (3) | |||||
| SE cost difference | 6086 | 7077 (14) | 6440 (5) | 6459 (5) | 6506 (6) | |||||
| z for CCA and t for MI | −2.100 | −2.010 | −2.090 | −2.140 | −2.030 | |||||
| p value | 0.036 | 0.045 | 0.037 | 0.032 | 0.042 | |||||
| 95 % CI lower limit | −24,720 | −28,085 | −26,057 | −26,489 | −25,954 | |||||
| 95 % CI upper limit | −865 | −345 | −810 | −1169 | −452 | |||||
| 35 % Missing data | ||||||||||
| n | 237 | 193 | 163 | 122 | 237 | 193 | 237 | 193 | 237 | 193 |
| Mean cost (euros) | 50,560 | 37,767 | 52,255 | 43,176 | 50,810 | 39,851 | 51,434 | 40,408 | 51,195 | 40,426 |
| SE mean (euros) | 5359 | 3063 | 6953 | 4560 | 5989 | 3448 | 5975 | 3601 | 6052 | 3551 |
| Treatment cost difference (euros) | −12,792 | −9080 (29) | −10,959 (14) | −11,026 (16) | −10,769 (16) | |||||
| SE cost difference | 6086 | 8463 (39) | 6853 (13) | 6988 (15) | 6954 (14) | |||||
| z for CCA and t for MI | −2.100 | −1.070 | −1.600 | −1.580 | −1.550 | |||||
| p value | 0.036 | 0.283 | 0.110 | 0.115 | 0.122 | |||||
| 95 % CI lower limit | −24,720 | −25,667 | −24,393 | −24,725 | −24,400 | |||||
| 95 % CI upper limit | −865 | 7508 | 2475 | 2673 | 2862 | |||||
| 50 % Missing data | ||||||||||
| n | 237 | 193 | 132 | 91 | 237 | 193 | 237 | 193 | 237 | 193 |
| Mean cost (euros) | 50,560 | 37,767 | 50,160 | 42,794 | 48,711 | 38,335 | 49,180 | 38,527 | 49,110 | 39,454 |
| SE mean (euros) | 5359 | 3063 | 7447 | 5336 | 5875 | 3513 | 5857 | 3501 | 5913 | 3683 |
| Treatment cost difference (euros) | −12,792 | −7366 (42) | −10,376 (19) | −10,653 (17) | −9656 (25) | |||||
| SE cost difference | 6086 | 9496 (56) | 6852 (13) | 6764 (11) | 6954 (14) | |||||
| z for CCA and t for MI | −2.100 | −0.780 | −1.510 | −1.570 | −1.390 | |||||
| p value | 0.036 | 0.438 | 0.130 | 0.115 | 0.165 | |||||
| 95 % CI lower limit | −24,720 | −25,978 | −23,810 | −23,912 | −23,289 | |||||
| 95 % CI upper limit | −865 | 11,246 | 3058 | 2607 | 3977 | |||||
M refers to the methadone maintenance treatment group, M + H refers to the group that had medical co-prescription of heroin. SE standard error, CI confidence interval, RA reference analysis, CCA complete case analysis, PMM multiple imputation with predictive mean matching, Log MI-PMM multiple imputation with predictive mean matching on log-transformed costs, Two-step-MI two-step multiple imputation with predictive mean matching