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2. Worldwide variation in prevalence of symptoms of asthma, allergic rhinoconjunctivitis, and atopic eczema: ISAAC;The International Study of Asthma and Allergies in Childhood (ISAAC) Steering Committee;Lancet,1998
3. The humane Society of the United States U.S. Pet Ownership Statistics, January 5th, 2007 http://www.hsus.org/pets/issues_affecting_our_pets/pet_overpopulation_and_ownership_statistics/us_pet_ownership_statistics.html
4. Pet Food Manufacturer’s Association Pet Statistics & Pet Ownership Trends http://www.pfma.com/public/petownership_stats.htm
5. Pet Net Pet Statistics http://www.petnet.com.au/petstatistics.asp