Table 2.

Definitions of Bluetooth measures and outcomes.

Measures/outcomes			Definition
Measuresa
	True positive	Bluetooth-identified contact that is confirmed by the participant
	True negative	No contacts detected, confirmed by the participant
	False positive	Bluetooth-identified contact denied by the participant
	False negative	Participant-recalled contact that was not detected by Bluetooth
Outcomes
	Sensitivity	True positive/(true positive + false negative)
	Specificity	True negative/(true negative + false positive)

^a15 minutes of interaction within 6 feet required to meet the definition of “close contact.” In addition to confirming/denying each close contact interaction, participants from the tag pilot were asked to comment on the underestimation or overestimation of the recorded contact duration. We allowed a 5-minute window of error, within which a contact’s measurement type could be altered. For example, a contact detected for 15-19 minutes would be designated as a false positive if the study participant noted that the interaction length was overestimated, while a contact detected for 10-14 minutes would be designated as a false negative if the study participant noted that the interaction length was underestimated.