Measured Results

The overall number of defects in Tetra Release 2 has decreased by 60%, in comparison to the number of defects detected in TETRA Release 1 (the reference line project). In part, this can be attributed to the fact that Release 2 is a continuation project and not an initial project as Release 1, and that later releases have usually less defects due to more cohesive teams, greater familiarity with the application domain, experience, and fewer undefined issues.

Based on numbers from other MCIL projects, we estimate that half of the defect decrease (30%) can be attributed to the implementation of the PIE.

A breakdown of the defects, by Phase of Origin, shows the following results :

Phase of Origin	TETRA Release 2 (# of defects = 40%)	Past Projects (# of defects = 100%)	% Improvement (in # of defects)
Requirement Spec.	20%	40.8%	80.6%
Preliminary Design	2.5%	11.8%	93%
Detailed Design	23%	23.9%	61.4%
Coding	54.5%	23.4%	8%
	100%	100%	60%

The obvious observation is that a higher percentage of the defects "moved" to later phases of the development process : from Requirement Specifications, Preliminary Design and Detailed Design, to Coding. In Tetra Release 1, 76.5% of the defects are in the Requirement and Design phases and only 23.4% are in Coding, while in Tetra Release 2, only 45.5% of defects are in Requirement and Design and 54.5% are in Coding. This implies that the defect prevention methods employed in the early phases of development were very effective.

The % Improvement column, shows the improvement within each development phase, with respect to the absolute number of defects. This is a different view of the improvement in the number of defects, partially attributable to the Improvement Actions.

Another comparison was made in respect to the Cause category. Following are the results :

Cause category	TETRA Release 2	Past Projects
Communication	10 %	11%
Education	13 %	13 %
Oversight	74 %	74 %
Transcription	3 %	2 %

The obvious observation here is that the differences are not significant.
The largest bulk of the defects are caused by human errors.

		Measured results
Implementation of the improvement actions				Lessons learned