The problem is that you randomly chose the stocks! You have no idea whether the stocks in these “best” funds performed better because they indeed are fundamentally better, or because you cherry-picked the best from a large set that simply varied in performance. If you flip 1,000 fair coins many times each, one of them will have come up heads much more than 50% of the time. However, choosing that coin as the “best” of the coins for later flipping obviously is silly. These are instances of “the problem of multiple comparisons,” a very important statistical phenomenon that business analysts and
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