Experimental design to persuade

A sender chooses ex ante how information will be disclosed ex post. A receiver obtains public information and information disclosed by the sender. Then he takes one of two actions. The sender wishes to maximize the probability that the receiver takes the desired action. The sender optimally discloses only whether the receiver's utility is above a cutoff. I derive necessary and sufficient conditions for the sender's and receiver's welfare to be monotonic in information. In particular, the sender's welfare increases with the precision of the sender's information and decreases with the precision of public information.