引用影響力研究中以百分等級正規化之缺點

Drawbacks of Normalization by Percentile Ranks in Citation Impact Studies

本文探討書目計量文獻中常被忽略之百分等級方法在引用影響力正規化上的缺點。此方法將引用次數轉換為百分等級，使數據由比率尺度轉變成次序尺度。然而，未定義兩值間的比率及兩值間的差異大小易導致重要資訊遺漏。由於在文獻集合中，以引用次數排序時，高被引文獻與其排序相鄰的文獻引用次數落差極大，且高被引文獻相較於非高被引文獻數量更為稀少，因而嚴重地扭曲了引用數據。此外，算術運算在次序尺度資料中是沒有意義的，這也排除了某些文獻所推薦的運算方式，如：用百分等級數據計算總和或是平均。本文以數個案例說明百分等級運算用於影響力指標將扭曲引用數據。

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.