MICHEL PIREU: Convenience trumps reality when we make our investment assumptions
Any element of the most credible conclusion is always up for questioning and never completely certain
Investment theories and broad generalisations are often based on convenience rather than real-world evidence. For example, a whole edifice of market theory has been built on the assumption that market prices are normally distributed. Yet every few years one or more markets experiences a price move that academics insist should only occur once in a million years, being so-many standard deviations from the “norm”.
One might think the repeated occurrence of these events would lead to the obvious conclusion that the price models don’t fit the real world. Instead they are dismissed as a rarity, unlikely to be repeated and better ignored. Convenience trumps reality. To make matters worse investors bring along their own sets of unsubstantiated beliefs that lead to misguided conclusions and flawed investment decisions. Among the more tenacious of these are the assumptions that:..
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