How a short sale affects credit is not an easy answer. For one, the industry has changed how it handles short sale deficiencies in the past four years. From my research, it appears borrowers with the best original credit score were affected the most and the borrowers who came out of the short sale with no deficiency reported did the best. Other factors are: amount of other revolving credit the borrower has, late payment history and type of loan (traditional, jumbo, FHA). Here's a few recent articles that try to answer the question in more detail.
Washington Post Article August 30, 2011