Function Points

Counting lines of code is but one way to measure size. Another one is the function point. Both are surrogate indicators of the opportunities for error (OFE) in the defect density metrics. In recent years the function point has been gaining acceptance in application development in terms of both productivity (e.g., function points per person-year) and quality (e.g., defects per function point).
In this section we provide a concise summary of the subject.

A function can be defined as a collection of executable statements that performs a certain task, together with declarations of the formal parameters and local variables manipulated by those statements (Conte et al., 1986).

The ultimate measure of software productivity is the number of functions a development team can produce given a certain amount of resource, regardless of the size of the software in lines of code.

The defect rate metric, ideally, is indexed to the number of functions a software provides.
If defects per unit of functions is low, then the software should have better quality even though the defects per KLOC value could be higher—when the functions were implemented by fewer lines of code. However, measuring functions is theoretically promising but realistically very difficult.