Why do Equally weighted indexes have small-cap bias?

Hi,

The CFAI text mentions that “Equal weighting also produces higher volatility than cap weighting, one reason being that it imparts a small-cap bias to the portfolio.”

Could someone please explain why equal weighting produces higher volatility and also why higher volatility imparts a small-cap bias?

Because small-cap stocks tend to have higher price volatility than mid-cap stocks and large-cap stocks.

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