Survey of the h index for all of academic neurosurgery: another power-law phenomenon?

Clinical article

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The h index is a recently developed bibliometric that assesses an investigator's scientific impact with a single number. It has rapidly gained popularity in the physical and, more recently, medical sciences.


The h index for all 1120 academic neurosurgeons working at all Electronic Residency Application Service–listed training programs was determined by reference to Google Scholar. A random subset of 100 individuals was investigated in PubMed to determine the total number of publications produced.


The median h index was 9 (range 0–68), with the 75th, 90th, and 95th percentiles being 17, 26, and 36, respectively. The h indices increased significantly with increasing academic rank, with the median for instructors, assistant professors, associate professors, and professors being 2, 5, 10, and 19, respectively (p < 0.0001, Kruskal-Wallis; all groups significantly different from each other except the difference between instructor and assistant professor [Conover]). Departmental chairs had a median h index of 22 (range 3–55) and program directors a median of 17 (range 0–62). Plot of the log of the rank versus h index demonstrated a remarkable linear pattern (R2 = 0.995, p < 0.0001), suggesting that this is a power-law relationship.


A survey of the h index for all of academic neurosurgery is presented. Results can be used for benchmark purposes. The distribution of the h index within an academic population is described for the first time and appears related to the ubiquitous power-law distribution.

Article Information

Address correspondence to: Matthew R. Quigley, M.D., Allegheny General Hospital, Department of Neurosurgery, 420 East North Avenue, Suite 302, Pittsburgh, Pennsylvania 15212. email:

Please include this information when citing this paper: published online May 14, 2010; DOI: 10.3171/2010.4.JNS091842.

© AANS, except where prohibited by US copyright law.



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    Box-and-whisker plots of the h indices for various levels of academic rank. The box represents the 25th to 75th percentile, the line within the box the median, and the bars all values except outliers. Academic ranks: 1 = professor; 2 = associate professor; 3 = assistant professor; and 4 = instructor.

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    Box-and-whisker plots of the h indices for departmental chairman (Chair) and program director (PD).

  • View in gallery

    Frequency distribution of all 1120 academic neurosurgeons by h index.

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    Plot of the rank order (100 − percentile, also cumulative frequency) versus h index, demonstrating exponential decay characteristic.

  • View in gallery

    Plot of the log of the rank versus the h index with the associated least-squares line.


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