A computer implemented method. A first synthetic event is received. The first synthetic event is derived from a first cohort comprising a first set of data and a second cohort comprising a second set of data. The first synthetic event comprises a third set of data representing a result of a mathematical computation on the first and second cohorts. A first rule set is created, the first synthetic event being expected as a result of application of the first rule set to the first cohort and the second cohort. The first rule set is applied to the first cohort and the second cohort to achieve a first result. The first result comprises a second event that is compared to the first synthetic event. A comparison is formed, the comparison comprising additional data that can be used to describe a difference between the second event and the first synthetic event.