Crown Indicator (CPP/FCSm)

The crown indicator, written CPP/FCSm, was the field-normalized citation impact measure developed at the Centre for Science and Technology Studies (CWTS) in Leiden and described by Moed, De Bruin, and Van Leeuwen in 1995. It compares a unit's observed citation rate with what would be expected given the fields, document types, and years in which it published. Specifically, it divides the citations per publication (CPP) by the mean field citation score (FCSm), forming a ratio in which a value of 1 marks performance exactly at the field average. For more than a decade it was CWTS's flagship indicator, until Waltman and colleagues showed in 2011 that its ratio-of-averages construction had statistical drawbacks and proposed the MNCS as a successor.