What's more, the work of Elroy Dimson, Paul Marsh and Mike Staunton of the London Business School has shown there is no statistical link between one year's economic growth and the next year's stockmarket returns.

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Amihud uses a statistical measure called "R-squared" to observe how much of active fund managers' returns can be explained simply by the index.

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In fact, three of the worst 10-year periods of real returns have come in the past six months, a record that practically begs for statistical redress.

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