Funding for this research was provided by:
Medical Research Council (MR/R024855/1, MR/R015600/1)
Received: 8 August 2018
Accepted: 29 May 2019
First Online: 20 June 2019
Ethics approval and consent to participate
: Not applicable. This study is an analysis of already published aggregated data so that no ethics approval or consent to participate is required.
: Not applicable.
: The authors declare that they have no competing interests.