Updates are available Correction dated 2016-02-16

Click to view Correction: https://0-doi-org.brum.beds.ac.uk/10.1186/s13063-016-1228-1

Updates are available Correction dated 2017-01-23

Click to view Correction: https://0-doi-org.brum.beds.ac.uk/10.1186/s13063-017-1787-9