Where can I find demographic data such as median household income for an area smaller that a zip code?

On August 17, 2011 Zillow Real Estate Research published an article on the historic ratios between housing prices and incomes. I would like to determine the ratio for the area that I live in but I can only find data for the entire city or by zip code. The zip code that I live in is split by a large Boulevard with a very nice area with expensive houses and a not so nice area. Where can I find median household income data for an area smaller than a zip code so I can calculate the housing price to income ratio? By the way, here's the link to the zillow article: http://www.zillow.com/blog/research/2011/08/17/what-goes-up-must-come-down-comparing-price-to-income-ratios-across-markets/.Where can I find demographic data such as median household income for an area smaller that a zip code?
a; a marketing research firm

b; a university's biz dept's professor

c; NAR [national assn of Realtors]



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