Janet Yellen says she doesn't want investors to rely on theFederal Reserve for explicit guidance on the next interest-ratehike—a communication strategy that's leaving some flatly confusedabout the path of monetary policy.

Speaking Monday in Philadelphia, the Fed chair said “only onrare occasions” will the central bank spell out when it's going tomove. “I really think the best we can legitimately do is explainwhat factors are guiding our thinking,” she told the audience,referring to the Fed's intention to make policy data-dependent.

Thechallenge with that approach is that it seems to be making itharder to understand the U.S. central bank's plans. Theirintentions are signaled in statements issued after eachrate-setting Federal Open Market Committee (FOMC) meeting, as wellas subsequent comments by its 17 policy makers that don'tnecessarily add up to a coherent explanation of Fed action.