Nassim Taleb has linked to a new paper on his Facebook Page: How We Tend To Overestimate Powerlaw Tail Exponents
October 2012
In the presence of a layer of metaprobabilities (from metadistribution of the parameters), the asymptotic tail exponent corresponds to the lowest possible tail exponent regardless of its probability. The problem explains “Black Swan” effects, i.e., why measurements tend to chronically underestimate tail contributions, rather than merely deliver imprecise but unbiased estimates.
Link: http :// www. fooled by randomness. com/ minexponents. pdf