(Bloomberg) -- Once-reliable tools for active managers are being sapped of their potency by an aging bull market, sending mutual funds to some of their worst relative returns in history.

So say Bank of America strategists, who found that stock selection based on normally bullish harbingers like buybacks, takeovers and activist interest didn’t work in the first half of 2016. Too much dependence on such signals worsened an already brutal year for large-cap managers, with only 18% beating the Russell 1000 Index through June 30, the research found.

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