[1] Univ Oxford, Ctr Evidence Based Intervent, Oxford OX1 2ER, England
[2] UCL, Ctr Outcomes Res & Effectiveness, Res Dept Clin Educ & Hlth Psychol, London WC1E 7HB, England
[3] Univ Oxford, Wolfson Coll Annexe, Ctr Stat Med, Oxford OX2 6UD, England
[4] Queens Univ Belfast, Inst Child Care Res, Belfast BT7 1LP, Antrim, North Ireland
[5] Ottawa Hosp, Ctr Practice Changing Res CPCR, Res Inst, Clin Epidemiol Program, Ottawa, ON K1H 8L6, Canada