The Corruption Perceptions Index (CPI) was established in 1995 as a composite indicator used to measure perceptions of corruption in the public sector in different countries around the world. During the past 20 years, both the sources used to compile the index and the methodology have been adjusted and refined. In 2012, important changes were made to the methodology to allow for score comparison across time, which was not possible prior to 2012.
The methodology follows four basic steps: selection of source data, rescaling source data, aggregating the rescaled data and then reporting a measure for uncertainty. The calculation process also incorporates a strict quality control mechanism which consists of parallel independent data collection and calculations conducted by two inhouse researchers and two academic advisors with no affiliation to Transparency International.