The Appraisal Assistant process assessment tool has been developed to support the assessment or appraisal of process capability and/or organizational maturity, following approaches consistent with the requirements of ISO/IEC 15504 and the Appraisal Requirements for Capability Maturity Model® Integration (CMMI®). In the course of an assessment a workload data file is captured containing information on the volume and usage of collected evidence in the assessment. This paper presents an analysis of evidence usage data from a total of 30 assessments employing a range of Process Assessment Models and Assessment Methods. Key differences between ISO/IEC 15504‐based and CMMI‐based assessments are identified, and some explanations of the differences are offered. Copyright © 2009 John Wiley & Sons, Ltd.