A metric has been developed for measuring privacy degradation when various types of media reveal private information about a person. The metric, which is based on joint entropy, quantifies accumulated revelations of information about various personal attributes. Application of this metric to entries posted on a social networking service and to leaks from a company database containing personal information showed that it is effective; that is, it can quantify accumulated revelations of information about multiple attributes and can cope with cases in which the attributes affect each other.