hat is Regime 1 and 2 stands for? why?

Smoothed Regime Probability ).8 ).9 Jan-94 Jul-94 Why Jan-95 Jul-95 Jan-96 Jul-96 Jan-97 Jul-97 Jan-98 Jul-98 Jan-99 Jul-99 Jan-00 Jul-00 Jan-01 Jul-01 Jan-02 Jul-02 Jan-03 Jul-03 Regime 1 Jan-04 Jul-04 Jan-05 Jul-05 Time-Series Smoothed Regime Probabilities and the MKT Risk Premium Series for the US Stock Market Date Jan-06 Regime 2 Jul-06 Jan-07 Jul-07 Jan-08 Jul-08 MKT Jan-09 Jul-09 Jan-10 Jul-10 Jan-11 Jul-11 Jan-12 Jul-12 Jan-13 Jul-13 Jan-14 Jul-14 Jan-15 Jul-15 Jan-16 Jul-16 Jan-17 Jul-17 5 0 -5 10 15 -10 -20 -15 Risk Premium