Investment Newsletter February 2020
Black swans & fat tails Back in the early 1600s, most Europeans knew one definitive fact about swans – swans are white. Every adult swan ever seen by a European was white, therefore (the logic goes) that all swans are white. Then Australia was discovered and with it a new species of swan… which was black.
Mike Deverell
Investment Manager Equilibrium Investment Management
A black swan is now a term we use to describe a highly improbable event that nobody anticipated and which can have a significant impact. In financial services, highly improbable events happen a lot more frequently than you might think!
Chart one on the next page shows the daily distribution of returns from the S&P 500 index (the blue bars). The fuzzy orange line shows what we call ‘normal distribution’, which is the way that standard mathematical probability models tells us returns ought to be distributed. What is clear is that there are a lot more returns in the middle than normal distribution would predict (a so called ‘thin peak’). If you look closely there are also a small number of blue bars (circled) towards far left and right of the chart. These are the much more extreme market moves of 4% or 5% in a day. Incidentally, the chart cuts
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