This author has mathematically correlated specific development practices to defect density and probability of on time delivery. This paper summarizes the results of this ongoing study that has evolved into a software prediction modeling and management technique. The author has collected data from 45 organizations developing software primarily for equipment or electronic systems. Of these 45 organizations, complete and unbiased delivered defect data and actual schedule delivery data was available for 17 organizations. The author will present in this paper the mathematical correlation between the practices employed by these organizations and defect density. This correlation can and is used to: a) Predict defect density b) Improve software development practices for the best return on investment.