Fig. 2

Example of performance analysis for initial contact detection (ICD) algorithms. The figure shows Initial contacts events identified by the reference system (IC-RS, depicted in black solid line) and initial contacts events identified by the single wearable device (IC-WD, depicted in orange dotted line). False Negatives, False Positive and True Positive events are defined with respect to the selected temporal tolerance window of 0.5 s (in grey) centred around the IC-RS. a Shows the identification of False Negative events (i.e., initial contact identified by the reference system but not identified by the single wearable device within the tolerance window) and False Positive events (i.e., initial contact wrongly identified by the single wearable device because although identified, it is outside the tolerance window). b Shows the identification of True Positives events (i.e., initial contact events correctly identified by the single wearable device) and example of other cases for identification of False Positive events (i.e., initial contact wrongly identified by the single wearable device). Note that the initial contact event, identified by the single wearable device, nearest to the true event (identified by the INDIP) will be considered a True Positive, and the rest of the identified events, False Positives. The figure also shows in blue how absolute errors are calculated only from True Positive events