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Effort Estimation KLOC is the only input variable. An exponential formula is used to calculate effort.

COCOMO Basic Effort Formula

Effort (E) = a x (Size)b
a and b = constants derived from regression analysis (depends ont eh project)
Size = thousands of lines of code (KLOC)
E = effort expressed in staff-months.

Effort is measured in staff-months (19 days per month or 152 working hours per month),  the constants a and b are determined by a curve fit procedure (regression analysis), matching project data tot eh equation. Most organization do not have enough data to perform such as analysis and begin by using Boehm’s three levels of difficulty that seem to characterize many software projects. Box 11-2 shows the basic formulas; lists the efforts and development time formulas for each mode.

The same-size project yields different amounts of effort when it is considered to be of different modes:

Suppose that a project was estimated to be 200 KLOC. Putting that data into the formula

Effort = a x (size)b

Basic COCOMO Effort Formulas for Three Modes

Effort for organic Mode : E = 2.4 x (Size)1.05
Effort for semidetached Mode : E = 3.0 x (Size)1.12
Effort for Embedded Mode : E = 3.6 x (Size)1.20

    Mode  a   b Effort Formula
Effort = a x (Size)b
Development Time
E = 2.4 x (S)1.05
E = 3.0 x (S)1.12
E = 3.6 x (S)1.20
TDEV = 2.5 x (E)0.38 Months
TDEV = 2.5 x (E)0.35 Months
TDEV = 2.5 x (E)0.32 Months

Effort for the organic mode would be estimated at 2.4 x (200)1.05 = 2.4 (260.66) = 626 staff-months.

Effort for the semidetached mode would be estimated at 3.0 x (200)1.12 = 3.0 (377.71) = 1,133 staff-months. Effort for the embedded mode would be estimated at 3.6 x (200)1.20 = 3.6(577) = 2,077 staff-months.

After effort is estimated, an exponential formula is also used to calculate a project duration, or completion time (time to develop, TDEV). Project duration is expressed in months.

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