We all hear about economic indicators all the time, but perhaps we don’t question them as much as we should. Take gross domestic product (GDP), which measures the growth of the economy. After a number of incremental but positive indicators that have come out in the past couple of months -- the so-called "green shoots" -- today's fourth quarter GDP was a reminder that our economy is still very fragile. And on the Marketplace Daily Pulse, union membership in the U.S. has plateaued.