Central bank says again that rates are likely to stay near zero through mid-2015.

Pledge to bolster job market could keep QE3 going until Fed chairman steps down in January 2014.

Pledge to bolster job market could keep QE3 going until Fed chairman steps down in January 2014.

Central bank considers tying low rates to economic data rather than the calendar.

Central bank considers tying low rates to economic data rather than the calendar.

Purchases to continue until jobs outlook improves substantially, Fed says.

Purchases to continue until jobs outlook improves substantially, Fed says.

Economists also expect FOMC to pledge to keep rates low into 2015.