Differences Between REVIC and COCOMO
The primary difference between REVIC and COCOMO is the set of basic coefficients used in the equations. REVIC has been calibrated using recently completed DoD projects and uses different coefficients. On the average, the values predicted by the basic effort and schedule equations are higher in REVIC versus COCOMO. The Air Force's HQ AFCMD/EPR published a study validating the REVIC equations using a database different from that used for initial calibration (the database was collected by the Rome Air Development Center). In addition, the model has been shown to compare to within +/- 2% of expensive commercial models (see Section 1.6).
Other differences arise in the mechanization of the distribution of effort and schedule to the various phases of the development and the automatic calculation of standard deviation for risk assessment. COCOMO provides a table for distributing the effort and schedule over the development phases, based on the size of the code being developed. REVIC provides a single weighted "average" distribution for effort and schedule, along with the ability to allow the user to vary the percentages in the system engineering and DT&E phases. REVIC has also been enhanced by using statistical methods for determining the lines of code to be developed. Low, high, and most probable estimates for each Computer Software Component (CSC) are used to calculate the effective lines of code and standard deviation. The effective lines of code and standard deviation are then used in the equations, rather than the linear sum of the estimates. In this manner, the estimating uncertainties can be quantified and, to some extent, reduced. A sensitivity analysis showing the plus and minus three sigmas for effort and the approximate resulting schedule is automatically calculated using the standard deviation.