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Since 1995, Transparency International (TI) publishes the Corruption Perceptions Index (CPI) annually ranking countries "by their perceived levels of corruption, as determined by expert assessments and opinion surveys." The CPI generally defines corruption as "the misuse of public power for private benefit."
As of 2010[update], the CPI ranks 178 countries "on a scale from 10 (very clean) to 0 (highly corrupt)."
|Corruption by country|
Transparency International commissioned Johann Graf Lambsdorff of the University of Passau to produce the Corruption Perceptions Index (CPI). The 2010 CPI draws on 13 different surveys and assessments from 10 independent institutions. The institutions are the African Development Bank, the Asian Development Bank, the Bertelsmann Foundation, the Economist Intelligence Unit, Freedom House, Global Insight, International Institute for Management Development, Political and Economic Risk Consultancy, the World Economic Forum, and the World Bank.
The 13 surveys/assessments are either business people opinion surveys or performance assessments from a group of analysts. Early CPIs used public opinion surveys. Countries must be assessed by at least three sources to appear in the CPI.
The CPI measures perception of corruption due to the difficulty of measuring absolute levels of corruption.
A study published in 2002 found a "very strong significant correlation" between the Corruption Perceptions Index and two other proxies for corruption; Black Market activity and overabundance of regulation. All three metrics also had a highly significant correlation with real gross domestic product per capita (RGDP/Cap). The Corruption Perceptions Index correlation with RGDP/Cap was the strongest.
The Corruption Perceptions Index has drawn increasing criticism in the decade since its launch, leading to calls for the index to be abandoned. This criticism has been directed at the quality of the index itself, and the lack of actionable insights created from a simple country ranking. Because corruption is wilfully hidden, it is impossible to measure directly; instead proxies for corruption are used. The CPI uses an eclectic mix of third-party surveys to sample public perceptions of corruption through a variety of questions, ranging from "Do you trust the government?" to "Is corruption a big problem in your country?"
The use of third-party survey data is a source of criticism. The data can vary widely in methodology and completeness from country to country. The methodology of the Index itself changes from year to year, thus making even basic better-or-worse comparisons difficult. Media outlets, meanwhile, frequently use the raw numbers as a yardstick for government performance, without clarifying what the numbers mean. A local Transparency International chapter disowned the index results after a change in methodology caused a country's scores to increase—media reported it as an "improvement". Other critics point out that definitional problems with the term "corruption" makes the tool problematic for social science.
The index mainly provides a snapshot of the views of business people and country analysts. In comparison, the questions in the Eurobarometer surveys 64.3 (2005), 68.2 (2007), 72.2 (2009), and the Flash Eurobarometer 236 (2008) established by the European Commission for all of the 27 European Union members states ask the perceptions and experiences of the general public. In general, the results show a very large divergence between the perception of living in a corrupt country by the general public and the experiences of corruption in everyday life.
Aside from precision issues, a more fundamental critique is aimed at the uses of the Index. As a source of quantitative data in a field hungry for international datasets, the CPI can take on a life of its own, appearing in cross-country and year-to-year comparisons that the CPI authors themselves admit are not justified by their methodology. The authors state in 2008: "Year-to-year changes in a country's score can either result from a changed perception of a country's performance or from a change in the CPI’s sample and methodology. The only reliable way to compare a country’s score over time is to go back to individual survey sources, each of which can reflect a change in assessment." 
The CPI produces a single score per country, which as noted above, cannot be compared year-to-year. In the late 2000s, the field has moved towards unpackable, action-oriented indices (such as those by the International Budget Partnership or Global Integrity), which typically measure public policies that relate to corruption, rather than try to assess "corruption" as a whole via proxy measures like perceptions. These alternative measures use original (often locally collected) data and so have the same non-comparability problem as the CPI and are limited in scope to specific policy practices (such as public access to parliamentary budget documents) and so they are only an indicator of visible corruption/policy corruption.
Research papers published in 2007 and 2008 examined the economic consequences of corruption perception, as defined by the CPI. The researchers found a correlation between a higher CPI and lower long-term economic growth, as well as a decrease in GDP growth of 1.7% for every unit increase in a country's CPI score. Also shown was a power-law dependence linking higher CPI score to lower rates of foreign investment in a country.
Worldwide Corruption Perceptions ranking of countries