Each month I calculate the strength of the US economy using a math based model I call RPA (Recession Probability Analytics). When the number rises above 50 it means the US economy is in the bottom 50% of all economic conditions relative to it history.
While far from perfect, the model has had an uncanny ability to correlate (negatively) with stock market returns. In other words, since I started publishing RPA the S&P 500 is just barely up (but very volatile), but when RPA has signaled less than 50 (the “green light” so to speak), the S&P 500 has risen over 50% (and not too volatile at all). I began publishing the model in November of 2007.