1. A computer implemented method for assessment of a user's cognitive function from mobile device usage, said method comprising the steps of: a. recording at a mobile computing device occurrences of inputs and timing of said inputs of user events including user interactions with applications resident on said mobile computing device; b. learning a function mapping from said recording to measurements of cognitive function that uses a loss function to determine relevant features in said recording, identifies a set of optimal weights that produce a minimum for said loss function, and creates said function mapping using said optimal weights; and c. applying said function mapping to a new recording of new occurrences of new inputs and timing of said new inputs of new user events including new user interactions with applications resident on the mobile computing device to calculate a new cognitive function value.