Scant Winners in S&P 500’s Record-Setting March Are Warning Sign

Fewer stocks are setting new highs alongside the S&P 500 Index, an unwelcome sign for traders worried about the market’s increasing concentration in a cluster of massive technology companies.

As the equity benchmark bounced to fresh records in recent weeks, the number of companies traded on the New York Stock Exchange making new highs outpaced those making new lows by only 88, an analysis by Oppenheimer & Co. showed. That’s been a harbinger of poor performance: since 1972, a difference of 100 or less while the S&P 500 broke out has resulted in subpar returns for the index, on ...