Table 4

SPC usage by group, hospital and period (planned subgroup analysis—quality and safety charts only)

Control group				Intervention group
Hospital	Preintervention	Postintervention	Post-Pre	Hospital	Preintervention	Postintervention	Post-Pre
Hospital	SPC/chart (%)	SPC/chart (%)	% difference	Hospital	SPC/chart (%)	SPC/chart (%)	% difference
1	2/23 (9)	0/16 (0)	-9	11	1/130 (0)	3/125 (2)	2
2	0/56 (0)	0/95 (0)	0	12	0/87 (0)	0/71 (0)	0
3	0/13 (0)	2/26 (8)	8	13	0/38 (0)	0/29 (0)	0
4	0/189 (0)	0/198 (0)	0	14	3/95 (3)	49/152 (32)	29
5	0/80 (0)	0/86 (0)	0	15	37/70 (53)	33/47 (70)	17
6	0/50 (0)	9/98 (9)	9	16	0/47 (0)	26/41 (63)	63
7	0/86 (0)	0/86 (0)	0	17	0/11 (0)	25/48 (52)	52
8	0/60 (0)	0/52 (0)	0	18	16/74 (22)	35/285 (12)	−10
9	0/40 (0)	1/44 (2)	2	19	0/50 (0)	19/46 (41)	41
10	5/60 (8)	0/40 (0)	−8	20	14/82 (17)	23/77 (30)	13
Total	7/657 (1)	12/741 (2)	1	Total	71/684 (10)	213/921 (23)	13
Average difference in control group (95% CI)			0 (−3 to 4)	Average difference in intervention group (95% CI)			21 (0 to 42)
				Average difference between intervention and control group* (95% CI)			18 (7 to 29)
				Average relative change between intervention and control group† (95% CI)			9 (2 to 41)

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. Subgroup analysis safety and quality charts only.
*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. Subgroup analysis safety and quality charts only.
SPC, statistical process control.