[1] Univ Surrey, Clin Informat & Hlth Outcomes Res Grp, Dept Hlth Care Management & Policy, Guildford GU2 5XH, Surrey, England
[2] UNSW Med Australia, Sch Publ Hlth & Community Med, Sydney, NSW 2052, Australia
[3] Univ Western Ontario, Schulich Sch Med & Dent, Western Ctr Publ Hlth & Family Med, Ctr Studies Family Med, London, ON N6A 5C1, Canada
[4] Royal Coll Gen Practitioners, London NW1 2FB, England