The defect prevention is to provide training whenever a new process or technology is introduced. LCL is set to zero when it is negative. The control chart is shown in Figure 4. An anomaly occurred in the fifth sample. Causal analysis revealed that data for that sample were for database code, all others were applications code.
Control charts require similar data for similar processes, i.e., apples to apples analogy.
The database sample was removed and the data charted again as shown in Figure 5. The root cause is that data gathered from dissimilar activities cannot be used on the same statistical process on control charts. Data from design cannot be combined with data from coding. The process for database design and code is different from that used for applications design and code as are the teams and methodologies. The defect prevention is against the process of collecting data for SPC control charts.