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Black Belt Brief

Service metric for bug resolution time


For software products, companies that provide rapid and accurate fixes to software problems have far higher customer satisfaction ratings than companies that produce defect-free software. This counter-intuitive finding demonstrates how highly customers are influenced by a vendor's problem resolution response time.

Most companies have no time-based service level agreement (SLA) for software defect resolution. The vendor's dilemma is that it is impossible to guarantee fix intervals for nasty bugs. Most support SLAs only commit to time-based escalation notifications within the vendor's organization. These workflows do little to satisfy a customer's primary concern about problem resolution responsiveness.

While it is impossible to guarantee a resolution time for any single bug, it is easy to determine an historical time-to-resolve average over a reasonable sampling of past bugs. Assuming past performance is an indicator of future performance, and allowing some margin for variances, one can construct a time-based SLA which provides the metrics customers value.

For example:

- 70 percent of severity one problems resolved within 10 days
- 80 percent of severity two problems resolved within 20 days
- Low severity problems resolved within the next two releases
- Guarantee applies to minimum contiguous sample of 50 problems


Graphically, the performance to the above SLA metric could look like the following chart.


The vendor's support organization reports monthly on the time taken to close customer problems. In any month, as long as there is a minimum of 50 resolved problems, the data is valid and plotted. Over time, the compliance goal can be ratcheted upward to further improve attention to problem resolution timeliness.

A similar chart could be created for an individual customer. (The time dimension might have to be changed to allow for the accumulation of a representative data set). Publishing individual customer and aggregated performance metrics can be a source of competitive advantage as well as enhance customer satisfaction.

Time based resolution metrics drive service and support teams towards better practices that have a huge impact on customer satisfaction. The statistical approach is a practical method to overcome traditional vendor reluctance to guarantee specific service levels.