You have to give Federal Reserve Chairman Ben Bernanke credit for standing his ground on data-dependence. Despite widespread suspicions, including on this blog, that the central bank would begin reducing the pace of its bond-buying stimulus in September simply because the markets were expecting it, the Fed chose to hold off in the face of a still-fragile economy.

Here’s how Bernanke addressed the issue of the market’s surprise at the Fed’s decision at his press conference:

I don’t recall stating that we would do any particular  thing in this meeting. What we are going to do is the right thing for the economy. And our assessment of the data since June is that, taken collectively, that it didn’t quite meet the standard of satisfying our – or of ratifying or confirming our basic outlook for, again, increasing growth, improving labor markets, and inflation moving back towards target. We try our best to communicate to markets – we’ll continue to do that – but we can’t let market expectations dictate our policy actions. Our policy actions have to be determined by our best assessment of what’s needed for the economy.

Still, even some Fed officials themselves have by now admitted the central bank did a poor job in communicating its message to markets in advance of the last meeting.

So, how wide is the Fed’s messaging gap? To get a rough measure, we can look at how much market expectations differed from central bank guidance at various points in time.