On the one hand, a fixed program size is straightforward to communicate; on the other hand, a program of fixed size cannot so easily adapt to changes in the economic outlook and the consequent changes in the need for policy accommodation.
In announcing its fixed-size programs, the FOMC did state a general willingness to do more if needed – and, indeed, it has followed through on that promise – but such statements left considerable uncertainty regarding the conditions that might warrant changes in an existing program or the introduction of a new one. 12  I discussed this effect more fully in Bernanke (2012).