It is better to follow sth. that works than not.
Past performance has little bearing to future performances.However, the chart works quite while from 2000 to 2011. It gives only 3 signals to exit (and 3 to reenter). That means only one false signal (and shortly a signal to return) which usually does not harm the portfolio except the tax consequences on taxable accounts.
The Complete Art of Investing only costs $10 for the Kindle version. Use it as a reference. It is a million dollar decision to many (me included). Everyone's risk tolerance is different. Being very conservative, I bet about 50% of my money on the hints currently.Yes, there are more false signals recently from the chart.
Every market is different. There are about 8 hints described such as interest rate. The indicator oil price turns out to be just the opposite in this market. I predicted the market would be positive in 2015. Why? From the statistics (or data mining or curve fitting) of the market performances for all years before election.
I exited the market in April, 2000 based on other hints. I did not in 2008 due to false security of my rising portfolio (with oil stocks), but reentered based on the chart. Hence, it is not totally curve fitting.