"The 2012 CPI draws on 13 different surveys and assessments from 12 different institutions. The institutions are the African Development Bank, the Bertelsmann Foundation, the Economist Intelligence Unit, Freedom House, Global Insight, International Institute for Management Development, Political and Economic Risk Consultancy, Political Risk Services, the World Economic Forum, the World Bank and the World Justice Project." (http://en.wikipedia.org/wiki/Corruption_Perceptions_Index)
Alex Cobham's Foreign Policy article explains it reflects "the opinions of an internationally focused elite, typically from a corporate background and perhaps a similar education". Preferable are alternatives where "a group of a country's citizens are considered instead of restricting the view to elite perceptions only". (http://www.foreignpolicy.com/articles/2013/07/22/corrupting_...)