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SSRN-Finiteness of Variance is Irrelevant in the Practice of Quantitative Finance by Nassim Taleb

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Paper written by NNT.

Finiteness of Variance is Irrelevant in the Practice of Quantitative Finance


Nassim Nicholas Taleb
NYU-Poly Institute; London Business School

June 09, 2008


Abstract:     
Outside the Platonic world of financial models, assuming the underlying distribution is a scalable power law, we are unable to find a consequential difference between finite and infinite variance models – a central distinction emphasized in the econophysics literature and the financial economics tradition. While distributions with power law tail exponents α>2 are held to be amenable to Gaussian tools, owing to their finite variance, we fail to understand the difference in the application with other power laws (1<α<2) held to belong to the Pareto-Lévy-Mandelbrot stable regime. The problem invalidates derivatives theory (dynamic hedging arguments) and portfolio construction based on mean-variance. This paper discusses methods to deal with the implications of the point in a real world setting.

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