1. CDFA (California Department of Food and Agriculture). 2011. 2011 California Dairy Statistics Annual. Accessed Dec. 19, 2013. http://www.cdfa.ca.gov/dairy/pdf/Annual/2011/2012_Annual_2011_Data.pdf
2. DHIA. 2009. Dairy Animal Care and Quality Assurance program. Accessed Dec. 19, 2013. http://www.bqa.org/CMDocs/bqa/DairyBQAManual.pdf
3. Mail and Internet Surveys: The Tailored Design Method;Dillman,2000
4. Elementary Survey Sampling;Scheaffer,1995
5. US Department of Agriculture. 2012. 2011 Certified Organic Production Survey. Accessed Dec. 19, 2013. http://usda01.library.cornell.edu/usda/current/OrganicProduction/OrganicProduction-10-04-2012.pdf