The CPI focuses on corruption in the public sector and defines corruption as the abuse of public office for private gain. The surveys used in compiling the CPI tend to ask questions in line with the misuse of public power for private benefit, with a focus, for example, on bribe-taking by public officials in public procurement. The sources do not distinguish between administrative and political corruption. The CPI Score relates to perceptions of the degree of corruption as seen by business people, risk analysts and the general public and ranges between 0 (highly corrupt) and 100 (highly clean).

Note: The time-series information in the CPI scores can only be used if interpreted with caution. Year-to-year shifts in a country's score can result not only from a changing perception of a country's performance but also from a changing sample and methodology. That is, with differing respondents and slightly differing methodologies, a change in a country's score may also relate to the fact that different viewpoints have been collected and different questions have been asked. Moreover, each country's CPI score is composed as a 3-year moving average, implying that if changes occur they only gradually affect a country's score. For a more detailed discussion of comparability over time in the CPI, see Lambsdorff 2005.

Note: In 2012 TI changed the methodology for which the data is not comparable and only data from 2012 and onwards can be compared.