(Bloomberg) -- Rob Arnott won't let it go.

One year after battling Cliff Asness in public over whether smart beta ETFs are in a bubble, the Research Affiliates co-founder is doubling down on his warning about the hugely popular investment vehicles. He's turning the firm's website into a new tool for telling which funds are about to pop and has launched a line of indexes that rejigger holdings based on variables like valuation.

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