1. Wennberg JE. Forty years of unwarranted variation--and still counting. Health Policy. 2014;114(1):1–2.
2. McCulloch P, Nagendran M, Campbell WB, Price A, Jani A, Birkmeyer JD, et al. Strategies to reduce variation in the use of surgery. Lancet. 2013;382(9898):1130–9.
3. Li Z, Zeki R, Hilder L, Sullivan EA. Australia's mothers and babies, 2011. Perinatal statistics series no. 28. Cat. no. PER 59. Canberra: AIHW National Perinatal Epidemiology and Statistics Unit; 2013.
4. Hospital Episode Statistics Analysis. NHS Maternity Statistics - England, 2012–13. Leeds: Health and Social Care Information Centre; 2014.
5. EURO-PERISTAT Project with SCPE and EUROCAT. European Perinatal Health Report. The health and care of pregnant women and babies in Europe in 2010. May 2013.