Humphrey, Kitson and Kasse have proposed that those who wish to evaluate the risks, productivity and quality associated with choosing a software vendor would be advised to examine the maturity level of the software processes employed. Humphrey's model, rooted in the quality control literature, has lacked empirical support An analysis of data collected in an extended software maintenance study has shown that the responses to Humphrey's key practice items fit the Rasch psychometric model. The authors offer an alternative growth interpretation based on their Rasch model analysis.