Abstract
OBJECTIVE: To investigate whether the h index (a bibliometric tool which is increasingly used to assess and appraise an individual's research performance) could be improved to better measure the academic performance and citation profile for individual healthcare researchers. DESIGN: Cohort study. SETTING: Faculty of Medicine, Imperial College London, UK. PARTICIPANTS: Publication lists from 1 January 2000 until 31 December 2009 for 501 academic healthcare researchers from the Faculty of Medicine. MAIN OUTCOME MEASURES: The h index for each researcher was calculated over a nine-year period. The citation count for each researcher was differentiated into high (h(2) upper), core (h(2) centre) and low (h(2) lower) visibility areas. Segmented regression model (sRM) was used to statistically estimate number of high visibility publications (sRM value). Validity of the h index and other proposed adjuncts were analysed against academic rank and conventional bibliometric indicators. RESULTS: Construct validity was demonstrated for h index, h(2) upper, h(2) centre, h(2) lower and sRM value (all P < 0.05). Convergent validity of the h index and sRM value was shown by significant correlations with total number of publications (r = 0.89 and 0.86 respectively, P < 0.05) and total number of citations (r = 0.96 and 0.65, respectively, P < 0.05). Significant differences in h index and sRM value existed between non-physician and physician researchers (P < 0.05). CONCLUSIONS: This study supports the construct validity of the h index as a measure of healthcare researcher academic rank. It also identifies the assessment value of our developed indices of h(2) upper, h(2) centre, h(2) lower and sRM. These can be applied in combination with the h index to provide additional objective evidence to appraise the performance and impact of an academic healthcare researcher.