Document is current

Article History

Accepted: 3 October 2017

First Online: 9 February 2018

Competing interests

: PJL, KW, JS, JW and PH conceived of the study. PJL, KW & JS secured funding. PJL, DP, KW and PH designed the study, with contributions from all authors. DP collected the data with assistance from KW and prepared the database. PJL and DP conducted the analyses. All authors had access to all of the data, including statistical reports and tables and can take responsibility for the integrity of the data and the accuracy of the data analysis. PJL drafted the manuscript, all authors reviewed and contributed to the final version.Patricia J Lucas is the guarantor for the study and affirms that the manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned (and, if relevant, registered) have been explained.Data sharing: ward level data and SPSS syntax are available from the corresponding author on request. Patient consent for data sharing was not obtained but the potential benefits of sharing these data outweigh the potential harms because data are fully anonymised and available at aggregate level only.The reporting of this study conforms to the The REporting of studies Conducted using Observational Routinely-collected health Data (RECORD) Statement.