1. Food and Drug Administration. http://www.fda.gov/downloads/Drugs/GuidanceComplianceRegulatoryInformation/Guidances/ucm072048.pdf
2. http://www.ich.org/LOB/media/MEDIA483.pdf
3. http://frwebgate3.access.gpo.gov/cgi-bin/PDFgate.cgi?WAISdocID=91506210980+3+2+0&WAISaction=retrieve
4. http://www.emea.europa.eu/pdfs/human/opiniongen/49892006en.pdf
5. Eligibility criteria of randomized controlled trials published in high-impact general medical journals;Van Spall;A systematic sampling review,2007