This document analyzes trends in software project productivity and cost drivers over 40 years using 341 projects. It finds that: 1) Productivity has increased overall and for both new development and maintenance projects. 2) A proposed "Difficulty" measure, combining the effects of COCOMO cost drivers, has decreased corresponding to increasing productivity. 3) Thirteen of twenty-two COCOMO cost drivers show significant correlation with completion year, influencing productivity trends. Platform and process factors like tools use and maturity improved while experience declined.