Plot the difference since 1979 between the Moodys Baa bond index (FRED code:BAA) and the U.S. Treasury

Question:

Plot the difference since 1979 between the Moody’s Baa bond index (FRED code:BAA) and the U.S. Treasury 10-year bond yield (FRED code:GS10). Comment on the trend and variability of this “credit risk premium” (Chapter) before and after the 2007-2009 financial crisis.