At maturity level 4, the organization and projects establish quantitative objectives for quality and process performance and use them as criteria in managing processes. Quantitative objectives are based on the needs of the customer, end users, organization, and process implementers. Quality and process performance is understood in statistical terms and is managed throughout the life of the processes [SEI 2001].

For selected subprocesses, detailed measures of process performance are collected and statistically analyzed. Quality and process-performance measures are incorporated into the organization’s measurement repository to support fact-based decision making [McGarry 2000]. Special causes of process variation are identified and, where appropriate, the sources of special causes are corrected to prevent future occurrences. (See the definition of “special cause of process variation” in the glossary.)

A critical distinction between maturity levels 3 and 4 is the predictability of process performance. At maturity level 4, the performance of processes is controlled using statistical and other quantitative techniques, and is quantitatively predictable. At maturity level 3, processes are typically only qualitatively predictable.