ABSTRACT
The purpose of this chapter is to validate the regional authority index (RAI). One can distinguish between two reasons for assessing (internal) validity of measurements. First, by validating measurements, commonalities come to the fore. In how far do the measures capture the same thing? This is how one usually understands assessing (internal) validity. Another reason, however, may lie in exploring differences between measurements. When do measures of the same concept disagree? The answer to this question reveals information that might be helpful in deciding when or how to use one or the other measurement. In this chapter the validity of the RAI is assessed by looking at the common alities as well as the differences between the RAI and other widely used, regionalization and decentralization indices.
