The Economist puts last week's stock market decline in context:
[H]ow predictive are big one-day falls of subsequent recession? Not very, as the chart below shows. In almost all big market falls since 1951 the crash has come in the midst of an economic recovery. In most cases, economic growth continued for several quarters after the crash, with the notable exception of the market collapse in October 2008, which was followed by recession.
A look at the predictive powers of longer-term market crashes here.
The Dish 