I believe the answer is: Formal method of audience analysis,
Formal method of audience analysis would be done by analyzing the behaviour that being done by the audiences when the speaker give the speech. From the behaviour, we can collect data regarding the audiences' preference that would help us appeal to similar audiences in the future.
The Americans won such an overwhelming victory because George Washington lead them to Trenton during the night to surprise attack the Hessians. The Hessians didn't even think the Americans were camped near them at all.