Table 4.

“Best Estimate” Event Prevalence and System Performance

Metric*	Derivation	Value (95% CI)
Prevalence
Case rate: proportion of cases with one or more true events	53 ÷ 1,000	0.053 (0.040–0.069)
Event rate: true events per case	65 ÷ 1,000	0.065 (0.051–0.082)
System performance for detecting cases with events
Sensitivity: proportion of cases with true events that had apparent events	15 ÷ 53	0.28 (0.17–0.42)
Specificity: proportion of cases with no true events that had no apparent events		0.985 (0.984–0.986)†
Positive predictive value: proportion of cases with apparent events that had true events	652 ÷ 1,461	0.45 (0.42–0.47)
Negative predictive value: proportion of cases with no apparent events that had no true events	930 ÷ 968	0.96 (0.95–0.97)
System performance for detecting individual events
Sensitivity: proportion of true events that were identified by the system	16 ÷ 65	0.25 (0.15–0.37)
Specificity: proportion of cases without true events of a given type that the system did not identify		0.9996 (0.9996–0.9997)†
Positive predictive value: proportion of apparent events that were true	704 ÷ 1,590	0.44 (0.42–0.47)
Negative predictive value: proportion of cases without true events of a given type that had no true event		0.9989 (0.9986–0.9992)

CI = confidence interval.

^*A true event was detected by manual review; an apparent event was identified by the system.

^†See the text for an explanation of the difference between case specificity and event specificity.