1. School of Public Health & Management, Chongqing Medical University; China Effective Health Care Network; No.1 YixueYuan Road Chongqing China 400016
2. World Health Organization; UNDP/UNFPA/UNICEF/WHO/World Bank Special Programme of Research, Development and Research Training in Human Reproduction (HRP), Department of Reproductive Health and Research; 20 Avenue Appia Geneva Switzerland 1211
3. Liverpool School of Tropical Medicine; Department of Clinical Sciences; Pembroke Place Liverpool Merseyside UK L3 5QA