Governments sometimes manipulate GDP data. For example GDP data can be manipulated through the calculation of price indexes. They can stop publishing important data prior to elections. They try to abolish independent statistics bureaus. They try to add questions that will bias responses to Census data. They leave in place price indexes known to be unreliable and impacting heavily and negatively on crucial pensions systems and so on.
The Transparency International Corruptions Perception rankings are used as a proxy for assessing the level of government corruption for each economy.
World Economics has converted the ranking data into an index on the scale from 0-100 where 0 is absolute corruption and 100 is no perception of government corruption.
Data source: Transparency International, Berlin, Index calculations by World Economics