Figure 7. WiFi similarity measures.

Positive predictive value (precision, ratio of number of true positives to number of positive calls, marked with dashed lines) and recall (sensitivity, fraction of retrieved positives, marked with solid lines) as functions of parameters in different similarity measures. A) In 98% of face-to-face meetings derived from Bluetooth, the two devices also sensed at least one common access point. D) Identical strongest access point for two separate mobile devices is a strong indication of a face-to-face meeting.