The definitions for each of the six

The definitions for each of the sixteen drivers, while not final, attempt to cover those activities which have the greatest impact on estimated Systems Engineering effort and duration. Each driver reflects the range of impact and variation assigned by the experts during our refinement exercises. The group of size drivers includes a volatility factor that accounts for the amount of change that is involved in the four factors. For example, it can be used to adjust the number of requirements should they be ill-defined, changing, or unknown at the time the estimate is being formulated. The group of cost drivers, also called Effort Multipliers, includes a schedule driver that accounts for the amount of schedule compression or expansion that might occur in a project. This schedule driver allows the user to increase the effort to reflect compressions made in the schedule for project related reasons.