Document is current

Article History

Received: 8 May 2018

Accepted: 16 September 2018

First Online: 26 September 2018

Ethics approval and consent to participate

: We used publicly available, aggregate country-level data from existing data sources; therefore, this analysis was not considered human subjects research and did not require ethical review. Participatory consent was not applicable.

: Not applicable.

: The authors declare that they have no competing interests.

: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.