"economists can’t predict recessions for the same reason stock market analysts can’t accurately predict market crashes. “Both kinds of events, by their nature, are not predictable events,Almost all the postwar recessions were preceded by a shock, It’s impossible to see the shocks coming” "
http://www.yomiuri.co.jp/national/news/20070305ic03.htm
経済、株価、ビジネス、政治のニュース:日経電子版
The Forecast for the Forecasters Is Dismal (Published 2007)