Yellen has said much, especially how the Fed Res is "data dependent." Yet, no one else can tell you upon what data Fed Res FOMC members depend. I can.
The economy is an effect. The cause is the state of bank credit.
The Fed Res exists for commercial banking and specifically, the largest commercial banks of the USA. The top three banks hold 36.5% of all bank assets. The top seven banks hold 50% of all bank assets. Yellen answers to the seven bankers who run those banks.
Yellen and friends at the FOMC depend on data from bankers and not the economy. Likely, Yellen and friends look at the data from the top seven banks to before they decide what to do.
All of the other data that publicly Yellen might talk about vaguely, such as unemployment, arise as effects from the state of banking. It is unlikely that any FOMC decision ever gets made because of employment data or any other data whatsoever except data from the top banks with respect to changes in assets and changes in loans.
As well, because four of the top ten U.S. banks have at least 20% of their assets outside of the USA, Yellen and friends consider the needs of those bankers. That is why in her presser after the last FOMC meeting, Yellen blathered something about looking at foreign economies.
If you want to see reality, you cannot go by current dollars. As well, you cannot rely on the bogus "real" chained dollars. It's impossible to deflate anything by an average of past inflated prices. For more on that see: Do You Still Believe That Inflation Means Rising Prices Rather Than Rising Bank Credit?
Yet, if you look at these charts, which you can see always in the World Economy League™, you should see that US banking has stabilized since the end of April, 2014. The Greatest Depression is coming to an end. The economy should return to normal cycles going forward beginning 2016.
It's also quite likely that you will not see another credit bubble such as the Greenspan-Bernanke Great Inflation, the greatest credit expansion in the history of mankind, in your lifetime. It's likely bankers learned quite well from the experience.
In True Dollars™, bank credit is up slightly as well as loans. This is what the FOMC jokers want to see.
It is the positive growth in loans in True Dollar terms that gives Yellen and friends confidence in lifting the FFR target after seven years of capital-destroying near ZIRP (see: Zirped! Bernanke and Now Yellen Have Felled Capitalism. Volker was Right on How to Do It).