The Beta Factor model is the most basic model. It assumes that all components belonging to a CCF group fail when that common cause occurs. By definition, this model distinguishes between individual failures and CCFs, with the assumption that if the CCF occurs, all components fail simultaneously by a common cause. Multiple independent failures are neglected. The input parameter and calculations for the unavailabilty of CCF events for the Beta Factor model are:

If n = 4, then the input parameter and calculations for the unavailability of CCF events would be: