  The impact of individual scientists is commonly quantified using
citation-based measures. The most common such measure is the h-index. A
scientist's h-index affects hiring, promotion, and funding decisions, and thus
shapes the progress of science. Here we report a large-scale study of
scientometric measures, analyzing millions of articles and hundreds of millions
of citations across four scientific fields and two data platforms. We find that
the correlation of the h-index with awards that indicate recognition by the
scientific community has substantially declined. These trends are associated
with changing authorship patterns. We show that these declines can be mitigated
by fractional allocation of citations among authors, which has been discussed
in the literature but not implemented at scale. We find that a fractional
analogue of the h-index outperforms other measures as a correlate and predictor
of scientific awards. Our results suggest that the use of the h-index in
ranking scientists should be reconsidered, and that fractional allocation
measures such as h-frac provide more robust alternatives. An interactive
visualization of our work can be found at https://h-frac.org
