Robert Arnott and his co-authors picked 100 portfolios, each with 30 equally-weighted stocks from the 1,000 largest American stocks by market capitalisation. 94 of the 100 “dartboard portfolios” did better than a market cap-weighted portfolio of all the 1,000 stocks. Similarly, in another study Andrew Clare, Nick Motson and Steve Thomas randomly picked American stocks to construct ten million indices. An additional twist to their experiment was that the stocks were also randomly weighted. Nearly all of the ten million "monkey indices” delivered “vastly superior returns” compared to a cap-weighted index.
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