Read this: Market strategist Phil Dow believes distinctions exist "between the current market malaise" and the Great Depression. He says the Dow Jones average's fall of more than 50% over a period of 17 months is similar to a 54.7% fall in the Great Depression, followed by a total drop of 89% over the following 16 months. "It's very troubling if you have a mirror image," said Dow. Floyd Norris, the chief financial correspondent of The New York Times, wrote in a blog entry in March 2009 that the decline has not been a mirror image of the Great Depression, explaining that although the decline amounts were nearly the same at the time, the rates of decline had started much faster in 2007, and that the past year had only ranked eighth among the worst recorded years of percentage drops in the Dow. The past two years ranked third, however.

How much did the Dow Jones average fall during a period of 17 months?
What is the answer? (If it cannot be answered, return "unanswerable")
50%