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Wednesday, January 28, 2009

John Kay: Simple enough!

Nice article by John Kay in the FT today. It's about using your brain and quitting this over reliance on financial models that do not assess economic conditions, but rather, base performance on indicators on a quantitative basis, only. You have to understand the situations behind the numbers.

The LSE taught me that. In fact, I dare to say that quantitative and analysis is an oxymoron.

"The model seems to be in question. But the idea behind it – that careful diversification can combine good returns with low risk – is as valid as ever. The problem is that some supporters of that approach put too much blame on sophisticated modelling techniques at the expense of their own knowledge and judgment. Banks made the same error in their risk assessments: their value-at-risk models had similar structure and origins to those in portfolio planning.

Quantitative portfolio management relies on measures of correlations between asset classes. These historical correlations are not universal constants but the products of particular economic conditions. Unless you understand the behaviour that produced them, you cannot assess their durability. In 2007-08, assets that had been uncorrelated were strongly correlated and many portfolio managers were surprised when the diversification they sought proved illusory.

Underlying causal relations had changed, as they frequently do in business. In the new economy bubble of the 1990s, equities roared ahead while property languished. But during 2003-2008, the availability of underpriced credit, followed by its abrupt withdrawal, affected property and shares in similar ways. Anyone in the financial world knew these things: but computers, churning through reams of data, did not.

Asset classifications change their meaning. The alternative asset classes that yielded strong returns in the 1990s for Harvard and Yale were hedge funds and private equity. But the increase in the number of hedge funds and the volume of their assets meant that an investment in the sector – once a bet on an individual’s idiosyncratic skills – became more similar to a general investment fund. Hedge fund returns were therefore increasingly correlated with those of other investments."
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