1. A computer-implemented means for assessing brain health of a person based on the person's use of a mobile device, wherein the computer-implemented means comprises a processing means, and wherein: the computer-implemented means receives inputs from a monitoring means installed on the mobile device, the inputs associated with one or more interactions of the person with the mobile device, the inputs recorded by the monitoring means without requiring additional actions by the person while the inputs are recorded; the computer-implemented means learns a function mapping from the received inputs to a brain health metric obtained from a brain test, wherein learning the function mapping uses a loss-function to determine relevant features of the inputs and to identify a set of optimal weights for the function mapping that produce a minimum of the loss-function; the computer-implemented means receives a set of new inputs from the monitoring means, the new inputs associated with one or more new interactions of the person with the mobile device; and the computer-implemented means applies the learned function mapping to the new inputs to calculate a new brain health metric.