1 / ((Ctrl.Gr.(w/ Cond) / Ctrl.Gr.(Total)) - (Act.Tx Gr.(w/ Cond) / Act.Tx Gr.(Total))
Ctrl.Gr.(Total) = No. of People in Control Group
Ctrl.Gr.(w/ Cond) = No. of People in Control Group who develop condition of interest during time interval
Act.Tx Gr.(Total) = No. of People in Active Treatment Group
Act.Tx Gr.(w/ Cond) = No. of People in Active Treatment Group who develop condition of interest during time interval
Calculator 
Formula 
