1. A method performed by a computer system for comparing event data sets comprising: calculating, by the computer system, one or more derivatives for each event in a first and second set of events; classifying, by the computer system, each event by respective calculated derivatives; and correlating, by the computer system, the first and second sets of events based on the classifications of the respective events; wherein each derivative is classified as a negative, zero or positive value and each event is classified according to a combination of negative, zero and positive values of the derivatives.