Further to an earlier post - Iraqi "Not Most Corrupt Country" - Roland Hodson commments:
On the [Transparency International] Corruption Index there is as you said considerable controvery. TI don't say exactly how they compile the index but I am sure that interviews with Multi-national companies would only be a part, probably a small part of their overall index. It is other survey's published by business risk organisations which only survey executives. Before TI started issuing their survey these were the only indexes of corruption available.
In Bangladesh TI has carried out massive and detailed studies of different government departments such as customs and ports and documented and measured the extent of the systematic corruption. I think you will find that the depth of the information and data that TI has varies considerably from country to country and depends on the funding and skill of their local offices and officers.
It is surprising to me that Iraq was judged to be on the same tier as Kenya and Pakistan. It would be helpful to everyone working for less corruption if TI would publish more of the data on which they base their ratings. That would help their index have more credibility.