Lifting the crown—citation z-score

Abstract

Researchers worldwide are increasingly being assessed by the citation rates of their papers. These rates have potential impact on academic promotions and funding decisions. Currently there are several different ways that citation rates are being calculated, with the state of the art indicator being the crown indicator. This indicator has flaws and improvements could be considered. An item oriented field normalized citation score average ( c ¯ f ) is an incremental improvement as it differs from the crown indicator in so much as normalization takes place on the level of individual publication (or item) rather than on aggregated levels, and therefore assigns equal weight to each publication. The normalization on item level also makes it possible to calculate the second suggested indicator: total field normalized citation score (Σ c f). A more radical improvement (or complement) is suggested in the item oriented field normalized logarithm-based citation z-score average ( c ¯ f z [ ln ] or citation z-score). This indicator assigns equal weight to each included publication and takes the citation rate variability of different fields into account as well as the skewed distribution of citations over publications. Even though the citation z-score could be considered a considerable improvement it should not be used as a sole indicator of research performance. Instead it should be used as one of many indicators as input for informed peer review.