10 Productivity Aphorisms

Correcting an error after delivery can be 100 times more expensive than correcting it during the requirement gathering phase
A time schedule can be compressed by up to 25%, but no more
One euro in development effort will amount to two euros in maintenance effort
Development and maintenance effort are mainly dependent on the size of the program in lines of code
Staff variability is the major cause behind development productivity variations
The ratio of software to hardware cost has changed from 15/85 in 1955 to 85/15 in 1985 and continues to expand
The ratio between design, development, and testing is approximately 60-15-25.
Software systems and products are three times as expensive as a stand-alone software problem
Testing will uncover 60% of the errors
Many software development phenomena and practices follow the 80/20 Pareto rule: 80% of the contribution is due to 20% of the contributors

(IEEE Software, Vol 4, No 5, Sept 1987, pp 84-85).