Table 1.

Performance indicators and metrics applied in evaluation of DEN systems

Performance indicator	Metric	WA notify estimates as of March 2022a
Reach
Number of installations within the population	Count of active and cumulative users measured by user installations	>3M activations, representing ∼51% of the adult WA population
Engagement
Utilization among infected users	Count of codes issued, claimed, keys published Attrition in user interface process	902 824 verification codes issued 76 936 diagnosis report started (codes claimed) 71 499 diagnosis report completed (keys published) 7.1% attrition of users who start diagnosis reporting process and do not finish
Utilization among exposed users	Count of ENs received, opened or dismissed	ENs opened (Web counter hits) = 742 336
Ratio of utilization among infected and exposed users	Ratio of exposures per diagnosis, measured as count of ENs opened per key published	7.9 ENs opened per diagnosis reported
Effectivenessa
Transmissions prevented	Model of cases averted	5500 infections prevented during the first 4 months
Transmission characteristics	Secondary attack rate (ie, the estimated proportion of individuals who develop COVID-19 among those who received an exposure notification)	Range of SAR used in cases averted modeling include 5.1%–13.7% during the first 4 months of WA Notify
Timeliness	Time from exposure-to-EN	5.3 days
Transmission characteristics	Adherence to quarantine reported in UX surveys	53% of WA Notify user survey respondents reported staying home after receiving an EN

^aThe effectiveness estimates are based on the November 2020–March 2021 cases averted analysis.