Table 2

Impact of chart design parameters on chart performance

Parameter	Change or unit amount	Sensitivity			Specificity			Youden’s index
Parameter	Change or unit amount	Shew	EWMA	MA	Shew	EWMA	MA	Shew	EWMA	MA
Baseline data (DICON vs local hospital)	Switch to DICON baseline	+0.111	+0.121	+0.114	NS	NS	NS	+0.109	+0.123	+0.121
Control limit widths (0.5–4 σ)	Per σ	−0.217	−0.213	−0.193	+0.239	+0.207	+0.122	+0.094	−0.006	−0.071
Baseline size (3–24 months)	Per month	+0.002	+0.002	+0.002	−0.002	−0.003	−0.003	NS	NS	NS
Baseline lag (0–24 months)	Per month	+0.002	+0.002	+0.003	+0.002	+0.002	+0.001	+0.004	+0.002	+0.001
Baseline type (fixed vs rolling)	Switch to fixed baseline	NS	−0.017	−0.020	+0.048	+0.046	+0.022	+0.038	+0.029	NS
Supplementary rules (yes vs no)	Switch to also use rules	+0.084	N/A	N/A	−0.028	N/A	N/A	+0.057	N/A	N/A
EWMA weight (0.2–0.8)	–	N/A	+0.089	N/A	N/A	−0.381	N/A	N/A	−0.292	N/A
MA span (3–12 months)	Per month	N/A	N/A	−0.008	N/A	N/A	+0.016	N/A	N/A	+0.008

Regression analysis results, conducted separately for each chart type. Values given are unstandardised regression coefficients. Change or unit amount denotes the change or increment size associated with each coefficient.
σ, estimated SD; DICON, Duke Infection Control and Outreach Network;EWMA, exponentially weighted moving average chart; MA, moving average chart; N/A, not applicable; NS, coefficient not statistically significant at the 0; Shew, Shewhart chart.