1. Armstrong BG: Optimizing power in allocating resources to exposure assessment in an epidemiologic study. Am J Epidemiol. 1996, 144: 192-197.
2. Hill AB: Observation and experiment. N Engl J Med. 1953, 248: 995-1001. 10.1056/NEJM195306112482401.
3. Edwards PJ, Roberts I, Clarke MJ, DiGuiseppi C, Wentz R, Kwan I, Cooper R, Felix LM, Pratap S: Methods to increase response to postal and electronic questionnaires. Cochrane Database Syst Rev. 2009, 3: MR000008-
4. International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use: ICH harmonised tripartite guideline, statistical principles for clinical trials E9.
http://www.ich.org/LOB/media/MEDIA485.pdf
5. CIOMS: Management of safety information from clinical trials: report of CIOMS working group VI. 2005, Geneva, Switzerland: Council for International Organisations of Medical Sciences (CIOMS)