Comparison of scientometric achievements at PhD and scientific output ten years later for 4,790 academic researchers

Abstract

Introduction: PhD is the highest awarded degree offered by universities in different disciplines. Owners of a PhD can teach at universities, start independent research and receive a higher salary while further building a scientific career. We examined whether the publication output before the PhD degree has a correlation with subsequent research activities.

Methods: We downloaded publication and citation data from the Hungarian Scientific Bibliography for Hungarian researchers who obtained PhD between the ages of 24 and 45. The researchers were grouped into eleven scientific sections. We examined the number of Q1 publications published in the previous 5 years, the H-index, the total number of citations for the last complete year, and the biological age of the researcher. Each parameter was computed for the year at which the PhD was obtained and ten years later. Pre-PhD publications (and citations for these) were excluded when assessing post-PhD track records. Spearman rank correlation and Kruskal-Wallis test were computed.

Results: We analyzed all together 4,790 researchers. We obtained a positive correlation between the number of Q1 publications before and after PhD (corr. coeff. = 0.21-0.54, p<0.01 in all sections), between the H-index before and after PhD (corr. coeff. = 0.32-0.56, p<0.01 in all sections), and between the citations received before and after PhD (corr. coeff. = 0.34-0.51, p<0.01 in all sections). All three metrics measured ten years after the PhD were negatively correlated with the age of the researcher at the time of obtaining the PhD (number of publications corr. coeff. = -0.09-0.22, p<0.05; H-index corr. coeff. = -0.09-0.29, p<0.08; number of citations corr. coeff. = -0.14-0.30, p<0.01). Among all disciplines, Philosophy and History and Engineering sciences show the strongest correlation between pre- and post-PhD output. When running multiple regression analysis for all three metrics as dependent variables and the number of articles, the H-index, the number of citations in the year of the PhD, the calendar year of PhD, and the gender of the researcher as independent variables, the number of articles and the H-index in the year of PhD reached the strongest positive correlations while gender had a negative correlation.

Conclusions: We independently evaluated pre- and post-PhD publication performance. In connection with age, the discipline-specific reference values of scientometric parameters at the time of obtaining the PhD can help to select candidates for postdoctoral grants and positions.

Fig 1. Publications before and after PhD were separately analyzed.

Fig 2. Flowchart of setting up the database up to the final cohort including 4,790 eligible researchers.

Fig 3

Average age at obtaining the PhD degree (A), number of publications in the previous five years (B), H-index (C), and yearly independent citations (D) at the year of obtaining the PhD in each scientific section. Mean and 95% CI are shown. See detailed data in S1 Table.