"Original reference: A.-L. Kinmonth, A. Woodcock, S. Griffin et al. 1998. Randomised controlled trial of patient centred care of diabetes in general practice: impact on current wellbeing and future disease risk. British Medical Journal, 317: 1202-1208."
"Source: M. J. Campbell and S. J. Walters. 2014. How to Design, Analyse and Report Cluster Randomised Trials in Medicine and Health Related Research. Chichester: John Wiley & Sons."