The higher the number of scores and the lower the variance of the results, the more trustworthy is the score for a particular country. However the figures we produce cannot be regarded as objective. Rather they represent the subjective evaluation of businessmen, risk analysts and the general public. With a low amount of surveys and a high variance the figures become weaker and special attention has to be put to the interpretation. An objective approach is almost impossible.
Corruption is by definition hidden.
There is of course objective data created by the justice system and the media. However, this data rather measures the effectiveness of the media in discovering and reporting scandals and how independent and well-trained the judiciary is in prosecuting. An efficient and incorruptible jurisdiction may result in a high rate of convictions. Six surveys are from 1997, with one going back to 1996. Nonetheless, the perception by contributors may refer back to experiences made long before the assessment is made.