1. A method of determining a measure of engagement of an audience for a presentation providing a sensory stimulus comprising: exposing the audience to the presentation over a period of time, wherein said period of time is divided into two or more time slots; providing a plurality of sensors, wherein the plurality of sensors measure a plurality of biologically based responses to said presentation for each member of the audience; providing a computer processing system adapted for receiving data relating to the presentation and data from the plurality of sensors; determining for each time slot at least one intensity value as a function of at least one of the measured biologically based responses; determining for each time slot at least one synchrony value as a function of a rate of change of at least one of the measured biologically based responses, wherein the synchrony value represents a number of audience members with the same or similar biologically based response for the at least one measured biologically based response; determining for each time slot at least one engagement value as a function of at least one of said intensity values and at least one synchrony value; and comparing the at least one engagement value to a database comprising stored engagement values to determine at least one indicator of success.