Using an event-study methodology, we investigate the effects of star recruitments on departmental and individual scientist productivity in three small open economies – Denmark, Ireland and New Zealand. The event is the arrival the star; and our dynamic methodology allows us to compare trends in productivity in the years before and after the star’s arrival, while controlling for various factors that affect the probability of a star’s arrival.
We find evidence of a large impact at the departmental level after a ‘star’ arrives – an average increase of approximately 20% in citation-weighted publication outputs after four years (see here). While we are cautious in treating this estimated effect as causal at the departmental level, our ability to identify control scientists in non-star-treated departments makes us more confident in making causal statements at the individual incumbent scientist level. At the individual level, we find an effect on citation-weighted scientific output of approximately 5% after four years.
In related work led by PhD student Anil Yadav, we examine one mechanism, which may help to explain this positive impact – co-authorship. The estimated effects of an incumbent scientist co-authoring with a star are significant. Interestingly, we find that creative productivity among incumbents who co-author with stars increases, even when we exclude the initial co-authored output from our study (see here).
Another mechanism through which stars might positively affect their new peers is through mentorship. Here, in work led by PhD student Akhil Sasidharan, we use the “paper trail” provided by the natural language processing of acknowledgement texts in published papers. Taking an acknowledgement as a (noisy) indicator of mentorship, we find evidence of a boost to productivity in the year the acknowledgment to a star occurs, but the productivity effect quickly fades unless there is evidence of sustained mentorship, indicated by acknowledgements to the star over multiple years.
In ongoing work led by post-doctoral researcher Jefferson Galetti, we are also exploring how the size of the star-arrival effect is mediated by how related the work of the star and incumbent are. We use various indicators to measure relatedness, e.g., an overlap of the journals in which they have published, and an overlap in the keywords listed on their publications. We hypothesise that increases in relatedness have both a positive effect (due to increase in the efficiency of knowledge exchange) and a negative effect (due to redundancy as the knowledge bases increasingly overlap).
Finally, we complement this quantitative analysis with a qualitative analysis based on interviews with stars recruited under the SFI Research Professorship Programme and the Niels Bohr Professorship Programmes in Denmark, led by Eoin Cullina of Atlantic Technological University. (1) The early results are consistent with the quantitative results above in pointing to factors that facilitate the engagement of recruited stars with their new peers.