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Article History

Accepted: 3 August 2025

First Online: 4 September 2025

Declarations

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: This work was supported by World Rugby Limited and the New Zealand Rugby Foundation (Grant number G-2004-00963). The study funders had no role in study conception or design, data collection, data analysis, data interpretation, or writing of the manuscript. World Rugby obtained an independent, external review of the project plan prior to funding.

: Financial interests: SD, BM, CL, SM, and TL’s research time was funded through their employment contracts with the University of Auckland, supported in part by the grant from World Rugby Limited. SD’s research time was also funded by the New Zealand Rugby Foundation. KQ has been employed by New Zealand Rugby since 2000 and currently occupies the role of Chief Scientist, New Zealand Rugby. He has received funding for travel and accommodation to attend World Rugby’s medical meetings. AJG is a contracted concussion consultant to Rugby Australia. He is the global clinical lead for the Word Rugby Brain Health Service. He has received travel funding or been reimbursed by professional sporting bodies and commercial organisations for discussing or presenting sport-related concussion research at meetings, scientific conferences, workshops, and symposiums. He has a clinical practice in neuropsychology involving individuals who have sustained sport-related concussion (including current and former athletes). He is supported by a National Health and Medical Research Council (NHMRC) Investigator Grant. He acknowledges unrestricted philanthropic support from the National Rugby League for research in former elite-level rugby league players. IM was employed by New Zealand Rugby from 2012 to 2019 as the Chief Medical Officer. Non-financial interests: KQ was a member of World Rugby’s Scientific Committee from 2014 to 2024, and has contributed to various World Rugby working groups focussed on player welfare issues from 2011 to the time of publication. His input into the project was conducted in collaboration with his co-authors, who are independent of New Zealand Rugby, and he declares that at no time did New Zealand Rugby, nor the funding agencies World Rugby and the New Zealand Rugby Foundation, provide advice or input into the data analysis, interpretation of the findings, or the manuscript preparation. A copy of the submitted draft of the project was provided to the funding bodies and New Zealand Rugby at the time of submission. AJG is a member of the World Rugby Concussion Working Group and the Australian Football League Concussion Scientific Advisory Committee. IM has held various committee appointments with World Rugby focused on player welfare matters. All other authors declare no relevant financial or non-financial interests.

: The data analysed in this study were housed in the New Zealand IDI, which is administered by Statistics New Zealand. Anonymised individual-level data in the IDI can only be accessed via secure data laboratories, and only export of approved aggregated results, as presented herein, is permitted under New Zealand privacy regulations. Permission to access data is only granted upon application to Statistics New Zealand as part of bona fide research projects. For these reasons, data cannot be made generally available. Note, these results are not official statistics. They have been created for research purposes from the IDI, which is carefully managed by Statistics New Zealand. For more information about the IDI, please visit . Access to the data was approved under project MAA2016-21.

: Ethics approval was granted by the Auckland Health Research Ethics Committee (ref. AH23203).

: Statistical code for analyses can be made available from the corresponding author upon request.

: CW and KQ conceived the project and digitised the data from the New Zealand Rugby Register so that it could be loaded into the New Zealand IDI. KQ, BM, SD, SM, CW, AG, IM, EV, and TL contributed to overall project planning and development of the funding application. Analyses were planned by SD, BM, KQ, FA, CL, TL, and SM. Analyses were conducted by FA, CL, SD, and BM. FA, KQ, SD, and BM drafted the report. All authors contributed to final drafting and editing and accept responsibility for the decision to submit the report for publication. Access to data for analyses in the IDI environment was restricted to CW, BM, FA, SD, and CL.