This is what I see using SPY since 2000 daily data. Chg is ABS(close-close[1]) TR is MAX(high-low, ABS(high-close[1], ABS(low-close[1])) 1 day ratio 5 day average of the ratio 2870 data point below 0.5 and 3513 data points above 0.5. 21 day average of the ratio 2600 data point below 0.5 and 3746 data points above 0.5. Plot of the SPY and the 21 days average of the ratio.
Identify trends is easy once you are in one. The real money is made by identifying when a trend starts and ends, in order to develop a positive expectancy method. Lag (group delay is the technical term) is the reason so many indicators do not work. A number of people have developed low/zero lag indicators for trend or reversion trading. I like the work of John Ehlers. Technical Papers
The 25% stat seems high More a historial analysis, not including the Trump Effect They Still Haven't Told You