IEG independently validates all completion reports that the World Bank prepares for its projects (known as Implementation Completion Reports, or ICRs). For a subset of completed projects (target coverage is 25%), IEG performs a more in-depth project evaluation that includes extensive primary research and field work. The corresponding ICR Reviews and Project Performance Assessment Reports (PPARs), codify IEG's assessments using Likert-scale project performance indicators. The World Bank Project Performance Ratings database is the collection of more than 8000 project assessments covering about 6000 completed projects, since the unit was originally established in 1967. It is the longest-running development project performance data collection of its kind.
The rating criteria has evolved through the years, from a single "Outcome" rating used early on, through the inclusion of additional ratings like "Bank" and "Borrower" performance, to the ten indicators used today. In 2005, IEG’s project performance ratings criteria and scales were harmonized with those used by World Bank operations, to ensure greater consistency between independent- and self-assessment of projects.