Making Software

Conclusion

This tells the story of over 25 years of evolution and tailoring the goals and processes for a particular environment. The continuous improvement was measured by taking values of three data points: the development defect rates, the reduced cost for development, and the improvement of reuse of code at three points in time: 1987, 1991, and 1995. Each data point represents the average of the three years around it [Basili et al. 1995]; see Table 5-1.

Table 5-1. The results of the QIP approach in the SEL

Continuous improvement in the SEL	1987–1991	1991–1995
Development defect rates	75%	37%
Reduced cost	55%	42%
Improved reuse	300%	8%

During this period there was a continual increase in the functionality of the systems being built. An independent study estimated it to be a five-fold increase from 1976 to 1992.

The cost of this activity was about 10% of the development costs. However, the data shows an order of magnitude improvement for that 10% cost, which is a pretty good ROI.

But the data in Table 5-1 are not the results of a controlled experiment or even a well-defined case study. One can argue that these results might have occurred anyway, even if we did nothing. There is no control group. But the people involved believe differently. We believe the learning process worked and delivered these results. No controlled experiment could have been developed for this 25-year study, as we did not know when we started what we would do and how it would evolve.

During the 25 ...