Although a stock price multiplier of about five for unanticipated changes in the federal funds rate is certainly not negligible, we should appreciate that unexpected changes in monetary policy account for a tiny portion of the overall variability of the stock market.
Unanticipated movements in the federal funds rate of 20 basis points or more are relatively rare (we observed only thirteen examples in our fourteen-year sample). Yet the change of one percent or so in the stock market induced by the typical 20-basis-point "surprise" in the funds rate is swamped by the overall variability of stock prices.