Defect prevention (DP) activities are intended to improve quality and improve productivity. It is now generally accepted that some defects present in the system will not be detected by the various QC activities and will inevitably find their way into the final system. Consequently, the higher the number of defects introduced in the software during development, the higher the number of residual defects that will remain in the final delivered system.
This point can be stated in another way. The overall defect removal efficiency of a process is the percentage of total defects that are removed by the various QC activities before the software is delivered. For a stable process, the defect removal efficiency is also generally stable. Hence, the greater the total number of defects in the system, the greater the number of defects in the delivered system. In other words, the higher the defect injection rate, the poorer the quality. Clearly, for a given process and its removal efficiency, the quality of the final delivered software can be improved if fewer defects are introduced while the software is being built. This recognition serves as the quality motivation for defect prevention.
DP also has productivity benefits. As discussed earlier, the basic defect cycle during the building of software is that developers introduce defects and later identify and remove them. In other words, something is introduced that is later removed. Clearly, this defect injection and removal cycle is a waste of effort it adds no value to the software. In this cycle, developers introduce something only to put in more effort to remove it (and they hope they remove all the errors). It therefore makes sense not to introduce defects in the first place; then the effort required to identify and remove them will not be needed. In other words, if you inject fewer defects, fewer defects must be removed; the effort required to remove defects, in turn, will be reduced, thereby increasing productivity. This concept serves as the cost motivation for DP.
How is DP done? The premise of DP is that there is some cause behind the injected defects. If the cause can be understood, efforts can be made to eliminate defects or minimize their impact. In other words, DP generally entails collecting data on defects found in the past, analyzing the data to find the root causes for the injection of the defects, and then developing solutions that attack the root causes.
Like any other major project task, the DP activities must be planned. You actually analyze defects and find solutions, however, after some amount of defect data from the project is available. To implement DP, a project manager may start with the set of recommendations available at the organization level and then build project-specific recommendations based on analysis of the project's defect data. At Infosys, the following steps are taken for defect prevention activities at the project level:
Identify a defect prevention team within the project.
Have a kick-off meeting and identify existing solutions.
Plan for defect prevention.
- Set defect prevention goals for the project.
- See that the DP team is trained on DP and causal analysis, if needed.
- Define the frequency at which defect prevention activities will be carried out.
Do defect prevention.
- At defined points, collate defects data.
- Identify the most common types of defects by doing Pareto analysis.
- Perform causal analysis and prioritize the root causes.
- Identify and develop solutions for the root causes.
- Implement the solutions.
- Review the status and benefits of DP at the project milestones.
- In the metrics analysis report and BOK, capture the learning and benefits you have obtained.
- Submit all outputs of DP as a part of the process assets.
During quality planning, your only activities are the planning activities. The activities under "Do defect prevention" or "Capture learning" are done while the project is executing or when it is finished. Here, we focus primarily on the tasks related to planning. Chapter 11 describes the tasks under "Do defect prevention" in a discussion of project monitoring.
Most of the activities relating to DP planning are self-explanatory. A project manager identifies a team that will perform the DP analysis (obviously, everyone in the project must perform the actual solutions that are to be executed to prevent defects). A kick-off meeting raises the awareness of team members and identifies the solutions that may be available in the organization. If needed, the DP team is trained on DP and causal analysis.
Setting the DP goals is a key planning activity. As mentioned earlier, DP is viewed as a strategy to achieve higher quality and productivity than the standard organization process can achieve. Hence, if a project manager has set quality and productivity goals that are higher than the organization level, as part of her strategy to achieve the goals she may use DP. In general, a project manager sets the DP goal in terms of reduction in the defect injection rate, typically about 10% to 20%. With this rate, its impact on quality and productivity can be estimated.
The other key planning activity is to decide when and how often DP tasks will be performed. Although a project manager can make these decisions, the general guideline at Infosys is that the DP activities should be carried out after about 20% of the programs have been coded, code reviewed, and unit tested, and again when about 50% of them have been coded, reviewed, and unit tested. That is, the first DP exercise is undertaken when the defect data from about 20% of the modules are available. Hopefully, the results of this DP should result in actions that will reduce the defect injection rate for the rest of the project. Then another DP exercise should be done at the 50% mark. In this exercise the project manager can determine whether the solutions are bearing results and whether further actions need to be taken. At this point of development, all the different types of defects should have been seen and their causes understood and acted on. Hence, further analysis will yield little new information.