Impact of chart design parameters on chart performance
Parameter | Change or unit amount | Sensitivity | Specificity | Youden’s index | ||||||
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.