Competing interests: All authors have completed the Unified Competing Interest form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author). We have read and understood BMJ policy on competing interests and declare that BH has received funding from the Commonwealth Fund through the Harkness Fellowship at The Dartmouth Institute of Health Policy and Clinical Practice (TDI) for the initial part of the research. The views presented here are those of the author and not necessarily those of the Commonwealth Fund their directors, officers, or staff or of TDI.