Funding for this research was provided by:
Medical Research Council (MR/K021680/1)
Received: 11 April 2019
Accepted: 20 August 2019
First Online: 25 September 2019
Ethics approval and consent to participate
: Institutional ethics approval was not sought because this is a retrospective study, and the databases are anonymised and free of personally identifiable information.
: Not applicable.
: The authors declare that they have no competing interests.