The Φ Index: Consolidating a Universal Citation Metric

We have previously [1] introduced the Φ index as a standardized, scale-independent, and field-normalized citation indicator that corrects for two types of biases that plague Journal Impact Factors: sensitivity to journal size and lack of field normalization. Here, we consolidate and extend the Φ index by performing extensive robustness checks, including confidence intervals, volatility estimates due to single-paper perturbations, and comparative evaluations with the Journal Impact Factor, the Journal Citation Indicator (JCI), and the Source Normalized Impact per Paper (SNIP). We further assess the sensitivity of Φ to different subject taxonomies, from journal-level subject categories of Journal Citation Reports (JCR) to paper-level classifications obtained through AI-assisted field assignment. The results confirm that Φ remains statistically stable across field boundaries and journal sizes, supporting its use as a robust, size- and field-invariant measure of journal citation performance.

[1] M. Antonoyiannakis. Φ index: A standardized scale-independent and field-normalized citation indicator (https://arxiv.org/abs/2401.00997)