FUND MANAGEMENT: Real life gets in the way of BSM certainty

The following article was published in Financial Times on December 10, 2007 and written by Pablo Triana, Director of  the Centre for Advanced Finance at IE. If you wish to learn more about our finance related programs, please visit http://www.miaf.ie.edu/.

The recent debate on the Black-Scholes-Merton options pricing model continues to make waves. Research by veteran option traders and authors Nassim Taleb and Espen Haug claims that BSM was not really an original invention, that its real-world popularity has been greatly exaggerated, and that there may be no mathematical models behind option prices, with simple supply-demand interaction claiming authorship instead.
Such bold statements, while a welcome contribution to the search for truth, may deprive us of something that seemed valuable. BSM, for all its flaws, offered quantifiable light where before there was only unknown darkness. By “losing” BSM, we would lose such certainty, albeit misplaced.
The most obvious certainty that the model offered was a precise number for the value of an option. This it did in a quite ingenious way. Everyone would tell you that an option should cost money because it gives you the right to enjoy a potentially large pay-out while limiting the possible losses if things do not go your way. But who ensures that that right has value per se? That value is supposed to come from the probability assigned to the option expiring in-the-money. So who guarantees that the probability of making money on the option is non-zero? Who can honestly claim to know the exact distribution governing financial assets? Pricing options based simply on probabilistic assumptions sounds a bit fishy.

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