The BCI index values lie between 0 and 100, with an increase in the index corresponding to a raise in the level of corruption. This is a first difference with CPI and WGI where an increase means that the level of corruption has decreased.

There exists no objective scale on which to measure the perception of corruption and the exact scaling you use is to a large extent arbitrary. However, we were able to give the index an absolute scale: zero corresponds to a situation where all surveys say that there is absolutely no corruption. On the other hand, when the index is one, all surveys say that corruption is as bad as it gets according to their scale. This is another difference with CPI and WGI, where the scaling is relative. They are rescaled such that WGI has mean 0 and a standard deviation of 1 in each year, while CPI always lies between 0 and 100.

In contrast, the actual range of values of the BCI will change in each year, depending how close countries come to the situation where everyone agrees there is no corruption at all (0), or that corruption is as bad as it can get (100).

The absolute scale of the BCI index was obtained by rescaling all the individual survey data such that zero corresponds to the lowest possible level of corruption and 1 to the highest one. We subsequently rescaled the BCI index such that when all underlying indicators are zero (one), the expected value of the BCI index is zero (hundred).