SEI maintanability index
The maintanability index represents the relative ease of maintaining the code.
This model consists of a number of easily calculated metrics, and is able to easily and quickly predict the maintainability of a software product.
The maintainability index is given as a polynomial equation composed of predictor variables. Through a series of studies it has been shown that there is a strong correlation between software maintainability and predictor variables such as McCabe's Cyclomatic Complexity, Halstead Volume, Number of Lines of Code, and Number of Code Comments.
Method of calculation
The equation to obtain the maintainability index is:
MISEI = 171 – 5.2 * ln(V) – 0.23 * CC – 16.2 * ln(LoC) + 50 * sin(sqrt(2.46 * perCM))
Where
V is the Halstead volume
CC is the cyclomatic complexity
LoC is the lines of code
perCM is the percentage of commented lines
History
The maintainability index (MI) is a software maintainability model proposed by Oman and Hagemeister at the University of Idaho (1991), originally presented at the International Conference on Software Maintenance ICSM 1992 and later refined in a paper that appeared in IEEE Computer.
The Software Engineering Institute (SEI) promoted this alternate formula in their 1997 C4 Software Technology Reference Guide. This report describes the Maintainability Index as "good and sufficient predictors of maintainability", and "potentially very useful for operational Department of Defense systems". Furthermore, they suggest that "it is advisable to test the coefficients for proper fit with each major system to which the MI is applied".
