SPC usage by group, hospital and period (all charts)
| Control group | Intervention group | ||||||
| Hospital | Preintervention | Postintervention | Post-Pre | Hospital | Preintervention | Postintervention | Post-Pre |
| SPC/chart (%) | SPC/chart (%) | % difference | SPC/chart (%) | SPC/chart (%) | % difference | ||
| 1 | 2/62 (3) | 0/81 (0) | −3 | 11 | 1/206 (0) | 9/225 (4) | 4 |
| 2 | 0/87 (0) | 0/127 (0) | 0 | 12 | 0/149 (0) | 0/131 (0) | 0 |
| 3 | 0/13 (0) | 2/119 (2) | 2 | 13 | 0/123 (0) | 0/84 (0) | 0 |
| 4 | 0/643 (0) | 0/687 (0) | 0 | 14 | 3/140 (2) | 91/256 (36) | 34 |
| 5 | 0/158 (0) | 0/170 (0) | 0 | 15 | 52/116 (45) | 47/67 (70) | 25 |
| 6 | 0/101 (0) | 15/179 (8) | 8 | 16 | 0/70 (0) | 58/81 (72) | 72 |
| 7 | 0/157 (0) | 0/151 (0) | 0 | 17 | 0/18 (0) | 27/67 (40) | 40 |
| 8 | 0/104 (0) | 0/101 (0) | 0 | 18 | 18/176 (10) | 42/457 (9) | −1 |
| 9 | 2/153 (1) | 6/200 (3) | 2 | 19 | 0/89 (0) | 27/86 (31) | 31 |
| 10 | 5/107 (5) | 0/85 (0) | −5 | 20 | 15/148 (10) | 27/113 (24) | 14 |
| Total | 9/1585 (0.6) | 23/1900 (1.2) | 0.6 | Total | 89/1235 (7) | 328/1567 (21) | 14 |
| Average difference in control group (95% CI) | 0 (−2 to 2) | Average difference in intervention group (95% CI) | 22 (2 to 42) | ||||
| Average difference between intervention and control group* (95% CI) | 17 (6 to 27) | ||||||
| Average relative change between intervention and control group† (95% CI) | 9 (3 to 32) | ||||||
For each hospital in preintervention and postintervention periods, the number of SPCs, the number of all charts and percentage of SPCs out of all charts are reported.
*T-test comparing average difference in proportions between intervention and control group. Percentage difference and 95% CI are reported.
†Zero-inflated negative Binomial regression models. Outcome is number of SPCs in postintervention period, adjusting for preintervention proportion of SPCs . Exposure is all charts. Risk ratios and 95% CI are reported.
SPC, statistical process control chart.