Interval Quality: Relating Customer-Perceived Quality to Process Quality

We investigate relationships among software quality measures commonly used to assess the value of a technology, and several aspects of customer perceived quality measured by interval quality (IQ): a novel measure of the probability that a customer will observe a failure within a certain interval after software release. We integrate information from development and customer support systems to compare defect density measures and IQ for six releases of a major telecommunications system. We find a surprising negative relationship between the traditional defect density and IQ. The four years of use in several large telecommunication products demonstrates how a software organization can control customer perceived quality not just during development and verification, but also during deployment by changing the release rate strategy and by increasing the resources to correct field problems rapidly. Such adaptive behavior can compensate for the variations in defect density between major and minor releases.