Dr. Foot is a metrics researcher. He examines the relationships between metrics and defect rates in order to determine which metrics relate to software quality. In order to carry out his work, he must have access to the source code of very large systems. This access is provided by the companies that developed the systems. In conducting his work, Dr. Foot discovered that programmer identity accounted for a large amount of variance in the defect rate. In other words, some programmers’ source code had many more defects than other programmers’. Dr. Foot mentioned the importance of programmer identity in his report, but refrained from revealing individual programmers’ identities or presenting any individuals’ defect data. Nonetheless, this did not preclude Dr. Foot from reporting a more general relationship between class complexity and defect rate.