45% of S&P 500 Stocks Now Carry a Negative Beta. Here Is the Index Math. By relifenomad No Comments on 45% of S&P 500 Stocks Now Carry a Negative Beta. Here Is the Index Math. 8 Min Read S&P 500 negative beta readings now cover about 45% of index members. Here is how cap weighting and low correlation let the index rise as many stocks fall.