Federal Reserve officials are moving into a more unpredictable phase of policy-making after two years of removing economic stimulus in regular, quarterly intervals.

They will be deciding whether and when to raise interest rates more on the basis of the latest signs of economic vigor -- such as in inflation, unemployment and growth -- and less on forecasts of how the economy is expected to perform in the months and years to come, they've indicated in interviews and public comments.

This could mean increased uncertainty for markets about the likely path of interest rates more than a few months or even weeks ahead.