PRIVACY PRESERVING DATA COLLECTION AND ANALYSIS

Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for preserving user privacy when collecting and analyzing user data. Methods include discarding user data after generating a privacy enhanced representation of user data and storing this privacy enhanced representation in a probabilistic data structure. Methods further preserve user privacy by inserting false negatives in the probabilistic data structure. Methods also include storing continuous value attributes in the data structure. Methods include storing date values associated with one or more user attributes. The date values may specify the date when one or more user attributes was last received.