Corruption Perceptions Index


The Corruption Perceptions Index is an index published annually by Transparency International, a German registered association, since 1995. It scores and ranks countries by their perceived levels of public sector corruption, as assessed by experts and business executives. The CPI generally defines corruption as an "abuse of entrusted power for private gain".
From 1995 to 2011, the index was scored on a scale of 10 to 0. Since 2012, the Corruption Perceptions Index has been ranked on a scale from 100 to 0.
Of the 180 countries ranked in the 2024 CPI, published in February 2025, the top scorers included Denmark, Finland, and Singapore, while those perceived as the most corrupt included South Sudan, Somalia, and Venezuela.
Although widely used as a key indicator of corruption, the CPI does not capture all forms of corruption. Perceptions about corruption may differ from actual levels of corruption and index focuses solely on the public sector. For a more comprehensive picture, the CPI should be used alongside other assessments.

Methods

The CPI methodology, revised in 2012, enables consistent comparison of corruption perceptions across countries and years. It involves four stages: selecting data sources, rescaling them to a uniform 0–100 scale, aggregating the results, and estimating uncertainty.

Selection of source data

The goal of the data selection is to capture expert and business leader assessments of various public sector corruption practices. This includes bribery, misuse of public funds, abuse of public office for personal gain, nepotism in civil service, and state capture. Since 2012 CPI has taken into account 13 different surveys and assessments from 12 different institutions. The institutions are:
Countries need to be evaluated by at least three sources to appear in the CPI. The CPI measures the perception of corruption due to the difficulty of measuring absolute levels of corruption.
Transparency International commissioned the University of Passau's Johann Graf Lambsdorff to produce the CPI. Early CPIs used public opinion surveys.

Rescaling source data

In order for all data to be aggregated into the CPI index, it is first necessary to carry out standardization during which all data points are converted to a scale of 0–100. Here, 0 represents the most corruption and 100 signifies the least. Indices originally measuring corruption inversely are multiplied by -1 to align with the 0–100 scale.
In the next step, the mean and standard deviation for each data source based on data from the baseline year are calculated. Subsequently, a standardized z score is calculated with an average centered around 0 and a standard deviation of 1 for each source from each country. Finally, these scores are converted back to a 0–100 scale with a mean of approximately 45 and a standard deviation of 20. Scores below 0 are set to 0, and scores exceeding 100 are capped at 100. This ensures consistent comparability across years since 2012.

Aggregating the rescaled data

The resulting CPI index for each country is calculated as a simple average of all its rescaled scores that are available for the given country, while at least three data sources must be available in order to calculate the index. The imputed data is used only for standardization and is not used as a score to calculate the index.

Reporting a measure for uncertainty

The CPI score is accompanied by a standard error and confidence interval. This reflects the variation present within the data sources used for a particular country or territory.

Related phenomena and indices

CPI and economic growth

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 higher long-term economic growth, as well as an increase 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 higher rates of foreign investment in a country.
The research article "The Investigation of the Relationship between Corruption Perception Index and GDP in the Case of the Balkans" from 2020 confirms the positive co-integration relationship in Balkan countries between CPI and GDP and calculates the affecting rate of CPI GDP as 0.34. Moreover, the direction of causality between CPI and GDP was identified from CPI to GDP and, according to this, the hypothesis that CPI is the cause of GDP was accepted.
The working paper Corruption and Economic Growth: New Empirical Evidence from 2019 emphasizes that many previous studies used the CPI for their analysis before 2012 and therefore may be biased. At the same time, it presents new empirical evidence based on data for 175 over the period 2012-2018. The results show that corruption is negatively associated with economic growth.

CPI and justice

As reported by Transparency International, there is a correlation between the absence of discrimination and a better CPI score. That indicates that in countries with high corruption, equal treatment before the law is not guaranteed and there is more space for discrimination against specific groups.
It seems that the country's justice system is an important protector of the country against corruption, and conversely, a high level of corruption can undermine the effectiveness of the justice system. Furthermore, as noted by the United Nations Office on Drugs and Crime, justice systems around the world are overburdened with large caseloads, chronically underfunded, and in need of more financial and human resources to properly fulfill their mandates. This, in combination with increasing outside interference, pressures and efforts to undermine judicial independence, results in the inability of justice systems to control corruption. The latest edition of the World Justice Project's Rule of Law Index, which shows that in the past year, justice systems in most countries exhibited signs of deterioration, including increasing delays and lower levels of accessibility and affordability, also serves as evidence of the urgency of the situation. Conversely, because corruption implies disproportionate favoring of some groups or individuals over others, it prevents people from accessing justice. For example, a person may rely on personal contacts to change a statutory process.
As shown in the Corruption Perception Index 2023, there is also a positive relationship between corruption and impunity. Countries with higher levels of corruption are less likely to sanction public officials for failing to adhere to existing rules and fulfill their responsibilities. A positive relationship was also shown between corruption and access to justice.

Other phenomena and indices

Thesis The Relationship Between Corruption And Income Inequality: A Crossnational Study, published in 2013, investigates the connection between corruption and income inequality on a global scale. The study's key finding is a robust positive association between income inequality and corruption.
A study from 2001 shows that the more affected by corruption, the worse a country's environmental performance. Measuring national environmental performance according to 67 variables, the closest match is with the 2000 TI Corruption Perceptions Index, which revealed a 0.75 correlation with the ranking of environmental performance.
A 2022 study titled "Statistical Analyses on the Correlation of Corruption Perception Index and Some Other Indices in Nigeria" investigated the relationship between the Corruption Perception Index in Nigeria and other relevant indices. These other indices included the Human Development Index, Global Peace Index, and Global Hunger Index. The result from the analysis carried out on the standardized data set shows that a positive linear relationship exists among all the variable considered except for CPI and GPI holding HDI and GHI constant which indicates a negative linear relationship between them.
A study investigating the relationship between public governance and the Corruption Perception Index found that aspects of public administration like voice and accountability, political stability, and rule of law significantly influence how corrupt a country is perceived to be. This suggests that strong governance practices can be effective in reducing corruption.

Criticism

The CPI has received significant criticism related to its conceptual and methodological limitations, and bias towards devoloped countries.
According to political scientist Dan Hough, three flaws in the Index include:
  • Corruption is too complex a concept to be captured by a single score. For instance, the nature of corruption in rural Kansas will be different from that in the city administration of New York, yet the Index measures them in the same way.
  • Measuring perception of corruption, rather than corruption itself, may reinforce existing stereotypes and cliches.
  • The Index only measures public sector corruption, ignoring the private sector. This, for instance, means the well-publicized Libor scandal, Odebrecht case and the Volkswagen emissions scandal are not counted as corrupt actions.
Media outlets frequently use the raw numbers as a yardstick for government performance, without clarifying what the numbers mean. The local Transparency International chapter in Bangladesh disowned the index results after a change in methodology caused the country's scores to increase; media reported it as an "improvement".
In a 2013 Foreign Policy article, Alex Cobham argues that the CPI reflects an elite bias in popular perceptions of corruption, potentially contributing to a vicious cycle and incentivizing inappropriate policy responses. Cobham writes, "the index corrupts perceptions to the extent that it's hard to see a justification for its continuing publication." He noted that "many of the staff and chapters" at Transparency International, "protest internally" over concerns about the index. The original creator of the index, Johann Graf Lambsdorff, withdrew from work on the index in 2009, stating that he was "no longer available for doing the Corruption Perceptions Index."
Recent econometric analyses that have exploited the existence of natural experiments on the level of corruption and compared the CPI with other subjective indicators have found that, while not perfect, the CPI is argued to be broadly consistent with one-dimensional measures of corruption.
In the United States, many lawyers advise international businesses to consult the CPI when attempting to measure the risk of Foreign Corrupt Practices Act violations in different nations. This practice has been criticized by the Minnesota Journal of International Law, which wrote that since the CPI may be subject to perceptual biases it therefore should not be considered by lawyers to be a measure of actual national corruption risk.
Transparency International also publishes the Global Corruption Barometer, which ranks countries by corruption levels using direct surveys instead of perceived expert opinions, which has been under criticism for substantial bias from the powerful elite.
Transparency International has warned that a country with a clean CPI score may still be linked to corruption internationally. For example, while Sweden had the 3rd best CPI score in 2015, one of its state-owned companies, TeliaSonera, was facing allegations of bribery in Uzbekistan.