German Centre for Higher Education Research and Science Studies (DZHW), Berlin, Germany ORCID: 0000-0001-5737-8483 donner@dzhw.eu
Abstract
This paper discusses drawbacks of the percentile rank method for citation impact normalization which have hitherto been neglected in the bibliometrics literature. The transformation of citation counts to percentile ranks changes ratio
scale data into ordinal scale data, for which the notions of the ratio between two values and of the magnitude of a difference between two values are not defined – a substantial loss of information. This distorts citation data particularly
severely because the differences between citation counts adjacent in order in publication sets are greater for more highly cited publications and because highly cited publications are more scarce than non-highly cited ones. Moreover,
arithmetic operations on ordinal scale data are not meaningful, which rules out arithmetic aggregations such as sums or averages for percentile rank data which are sometimes recommended in the literature. Distortion of citation data
by aggregating percentile ranks for average impact indicators is demonstrated with several examples.
Keywords
Citation Normalization; Field Normalization; Percentile Ranks; Ordinal Data
