The recent drop in the stock market, if it persists, will present serious challenges for the Yellen Fed.
In a couple of recent academic papers, The Stock Market Crash of 2008 caused the Great Recession: Theory and Evidence here and The Stock Market Crash Really Did Cause the Great Recession here I showed that changes in the value of the stock market cause changes in the unemployment rate three months later. Here is a link to a Freakonomics post that features my work.
I continue to receive requests for the data that I used in those studies. That data is available here. These are important empirical findings that establish a strong and stable relationship between changes in the value of the S&P and changes in the U.S. unemployment rate.