After the exceptional performance of large-cap stocks in recent years, concentration concerns naturally come to mind.
There are many ways to measure concentration. A simple method is to add up the weight of the top names, but the drawback with this approach is it doesn’t incorporate all the constituents in an index. The Herfindahl-Hirschman Index (HHI), defined as the sum of the squared index constituents’ percentage weights, is more favorable from this aspect and is widely used.
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