Principle 3: Productivity and quality are inseparable
There is a clear relationship between productivity (measured by numbers of widgets - wheter they be lines of code or function points - per person-month) and quality. The higher the demand for quality, the lower your productivity becomes. The more you emphasize increased productivity, the lower your resulting quality.
Bell Labs has found that, to achieve one to two bugs per thousand lines of code, productivities of 150 to 300 lines of code per person-month are common [see Fleckenstein, W., “Challenges in Software Development”, IEEE Computer, 16, 3 (March 1983), pp. 60-64]. As attempts are made to drive productivity up, the density of bugs increases.
 Lehman, M., “Programming Productivity-A Life Cycle Concept,” COMPCON 81, Washington, D.C.: IEEE Computer Society Press, 1981, Section 1.1.