Funding for this research was provided by:
National Institute for Health Research
Received: 7 March 2018
Accepted: 20 June 2018
First Online: 2 August 2018
Ethics approval and consent to participate
: Not applicable, the anonymised secondary data analysed in this study are published by NHS Digital, used under the terms of the Open Government Licence.
: Not applicable, no individual person’s data is included in the manuscript.
: The authors declare that they have no competing interests.
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