A method of responding to a criterion-based request for information collected from users meeting the criterion while complying with a user-requested privacy requirement. In one embodiment a request is received for data comprising facial or audio expressions for users who meet the criterion. A program monitors activities indicative of user attention or user reaction based on face tracking, face detection, face feature detection, eye gaze determination, eye tracking, audio expression determination, or determination of an emotional state. When a user requests a high level of privacy, the timestream data collected for the user is aggregated with timestream data collected for other users into a statistical dataset by processing the timestreams to ensure the high level of privacy in the statistical dataset which is provided to a content provider without providing data collected for the user who has requested the high level of privacy.