Received: 28 July 2019
Accepted: 5 November 2019
First Online: 14 November 2019
Ethics approval and consent to participate
: Not applicable [Based on a statement declared by the University of Sheffield, the research ethics approval not required for a project which will only use publicly available anonymized data obtained from large national data sets. URL: ExternalRef removed].
: Not applicable.
: The authors declare that they have no competing interests.