Acknowledgements Partial funding was provided by AHRQ
through a contract to RAND (HHSA-290-2007-10062I) and by
the Clinical and Translational Science Award (CTSA)
programme, previously through the National Center for
Research Resources (NCRR) grant 1UL1RR025011, and now
by the National Center for Advancing Translational Sciences
(NCATS), grant 9U54TR000021. The content is solely the