Yellen's yo-yo effect on stocks: More to come?

NEW YORK -- Leadership transitions at the Federal Reserve have a history of causing financial market gyrations. The most famous market dive after a changing of the guard at the Fed occurred in 1987, when stocks crashed in October, three months after then-Fed chairman Alan Greenspan took over for Paul Volcker.
Turbulence related to a new top gun at the Fed returned to Wall Street Wednesday.
A comment by new Fed Chair Janet Yellen at her first press conference, suggesting the Fed could start raising short-term interest rates "six months" after it ends its bond-buying program, sparked a sell-off in stock and bond markets. Her comments were interpreted as a sign that rates would rise sooner than Wall Street had anticipated. Whether that takeaway was accurate, it created confusion about the timing of the Fed's exit strategy.
Does that mean the transition from ex-Fed chief Ben Bernanke to Yellen will spell a rocky period for stocks? Not necessarily, history says.
While a leadership change at the Fed is believed to cause stocks to lose altitude and volatility to spike, data tell a less sinister story, says Bespoke Investment Group. The median gain of the S&P 500 stock index in the first year of a Fed chair's term since 1948 is 13.1%, better than the average 8.5% gain for all periods. The biggest median decline during year one is 5.8%, vs. an average drop of 8.7%. The takeaway: It is Fed policy, not personalities, that moves markets most.