Figure 4. Four-fold cross validation.

A) Activity tracking accuracy. The location-known analysis builds classifiers using clips from one phone location, and tests each classifier with clips only from its respective location. The location-assumed analysis builds classifiers using clips from one phone location, but tests each classifier with clips from all four locations. The global model builds a classifier with clips from all the phone locations, and tests the classifier with clips from all locations. The joint classifier is built and tested using activity-location pairs; the accuracies shown here are marginalized over each phone location. B) Location tracking accuracy. Each analysis is analogous to the activity tracking, except the classifiers are now trained and tested to predict the location of the phone.