Mapping the global neurosurgery workforce. Part 2: Trainee density
Authors: Gupta Saksham , Gal Zsombor T. , Athni Tejas S. , Calderon Chrystal , Callison William É , Dada Olaoluwa E. , Lie Winston , Qian Carolyn , Reddy Ramya , Rolle Myron , Baticulon Ronnie E. , Chaurasia Bipin , Dos Santos Rubio Ellianne J. , Esquenazi Yoshua , Golby Alexandra J. , Pirzad Ahmad F. , Park Kee B. , _ _ , Cheserem Jebet B. , El Ouahabi Abdesaamad , Khan Tariq , Kolias Angelos , _ _ , Demetriades Andreas K. , Rasulic Lukas , Foroglou Nicolas , Garozzo Debora , Gonzalez-Lopez Pablo , Ivanov Marcel , Lafuente Jesus , Marchesini Nicoló , Olldashi Fatos , Paterno Vincenzo , Petr Ondra , Rotim Kresimir , Rzaev Jamil , Timothy Jake , Tisell Magnus , Visocchi Massimiliano , _ _ , Esene Ignatius , Qureshi Mubashir M. 
Published: January 2024

OBJECTIVE
A sustainable neurosurgery workforce depends on robust training pipelines, but the size and distribution of the global neurosurgery trainee workforce has not been described. The objective of this study was to identify the types of training programs that exist in the global neurosurgery workforce, the support that trainees receive, the diversity of trainee experiences, and the accreditation processes that exist to regulate training programs.

METHODS
This study was a subanalysis of a cross-sectional survey administered online in all 193 countries and 26 territories, independent states, and disputed regions as defined by the World Bank and United Nations. Participants were identified through neurosurgery society leadership, the personal contacts of the coauthors, and bibliometric and search engine searches. Population-weighted statistics were constructed and segregated by country income level and WHO regions.

RESULTS
Data were obtained for 187 countries (96.9%) and 25 additional territories, states, and disputed regions (96.2%). There were an estimated 1261 training programs and 10,546 trainees within the regions sampled, representing a global pooled density of 0.14 neurosurgery trainees per 100,000 people and a median national density of 0.06 trainees per 100,000 people. There was a higher density in high-income countries (HICs; 0.48 trainees per 100,000 people) compared with upper-middle-income countries (0.09 per 100,000), lower-middle-income countries (0.06 per 100,000), and low-income countries (LICs; 0.07 per 100,000). The WHO European (0.36 per 100,000) and Americas (0.27 per 100,000) regions had the highest trainee densities, while the Southeast Asia (0.04 per 100,000) and African (0.05 per 100,000) regions had the lowest densities. Among countries with training programs, LICs had the poorest availability of subspecialty training and resources such as cadaver laboratories and conference stipends for trainees. Training program accreditation processes were more common in HICs (81.8%) than in low- and middle-income countries (LMICs; 69.2%) with training programs.

CONCLUSIONS
The authors estimate that there are at least 1261 neurosurgery training programs with 10,546 total trainees worldwide. The density of neurosurgery trainees was disproportionately higher in HICs than LMICs, and the WHO European and Americas regions had the highest trainee densities. The trainee workforce in LICs had the poorest access to subspecialty training and advanced resources.