We know corruption is a problem around the world. But how bad is it and what can be done? The Corruption Perceptions Index measures the perceived levels of public sector corruption in countries worldwide. Based on expert opinion, countries are scored from 0 (highly corrupt) to 100 (very clean). Some countries score well, but no country scores a perfect 100. Two-thirds of the 176 countries ranked in the 2012 index score below 50, showing that public institutions need to be more transparent, and powerful officials more accountable.