this end, for a given defect type, defect distributions across development stages are compared with the baseline rates. For each chain of results—say, too high early on, lower later, and high at the end—an implication is derived. For example, the implication may be that function testing should be revamped.

This methodology has been extended to a study of the distribution of triggers, that is, the conditions that allow a defect to surface. First, it is implicit in this approach that there is no substitute for a good data analysis. Second, assumptions clearly are being made about the stationarity of reference distributions, an approach that may be appropriate for a stable environment with similar projects. Thus, it may be necessary to create classes of reference distributions and classes of similar projects. Perhaps some clustering techniques may be valuable in this context. Third, although the defect types are mutually exclusive, it is possible that a fault may result in many defects, and vice versa. This multiple-spawning may cause serious implementation difficulties. Proper measurement protocols may diminish such multipropagation. Finally, given good-quality data, it may be possible to extend orthogonal defect classification to efforts to identify risks in the production of software, perhaps using data to provide early indicators of product quality and potential problems concerning scheduling. The potential of this line of inquiry should be carefully investigated, since it could open up an exciting new area in software engineering.

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