The Bayesian Corruption Index is a composite index of the perceived overall level of corruption: with corruption refered to as the ``abuse of public power for private gain''. Perceived corruption: Given the hidden nature of corruption, direct measures are hard to come by, or inherently flawed (e.g. the number of corruption convictions). Instead, we amalgamate the opinion on the level of corruption from inhabitants of the country, companies operating there, NGOs, and officials working both in governmental and supra-governmental organizations. Composite: it combines the information of 20 different surveys and more than 80 different survey questions that cover the perceived level of corruption.
It is an alternative to the other well-known indicators of corruption perception: the Corruption Perception Index (CPI) published by Transparency International and the Worldwide Governance Indicators (WGI) published by the World Bank. Methodologically, it is most closely related to the latter as the methodology used in the construction of the BCI can be seen as an augmented version of the Worldwide Governance Indicators' methodology.
The augmentation allows an increase of the coverage of the BCI: a 60% to 100% increase relative to the WGI and CPI, respectively. In addition, in contrast to the WGI or CPI, the underlying source data are entered without any ex-ante imputations, averaging or other manipulations. This results in an index that truly represents the underlying data, unbiased by any modeling choices of the composer.
The overall correlation between the 2023 and 2018 BCI index as well as the 2023 BCI and the WGI's control of corruption, is high (>94%). However, for a given country, the changes over time can be quite drastically different. The changes are due to alterations that were made to the underlying database of corruption indicators (partly corrections, partly due to restrictions in data access). The list of indicators per source will also be updated on the website; you can follow them at http://users.ugent.be/~sastanda/BCI/BCI.html