[isatrader]

I'd have a look at some individual charts to confirm the data, as from a quick visual check of 2020 for example, I'm seeing more stocks above their Mansfield RS zero line than not when looking at the Nasdaq 100 stocks for example. This is just a quick visual check mind. But the Percentage above their Mansfield RS zero line in your chart seems far too low.

I've attached the Russell 3000 etf for example, which shows that it was above the Mansfield RS zero line from May 2020 to August 2021, so the individual stocks within the index should have been above 50% imo if the index etf is outperforming the S&P 500, as it's an average of the stocks. But if you look at the NYSE index it underperformed through 2020, while the Nasdaq Composite massively outperformed. So it could just be that your data is focused mostly on the NYSE.