Blog Archives

The look of verifying data

October 7, 2013
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The look of verifying data

Get data that fit before you fit data. Why verify? Garbage in, garbage out. How to verify The example data used here is daily (adjusted) prices of stocks.  By some magic that I’m yet to fathom, market data can be wondrously wrong even without the benefit of the possibility of transcription errors.  It doesn’t seem … Continue reading...

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Changeability of Value at Risk estimators

August 26, 2013
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Changeability of Value at Risk estimators

How does Value at Risk change through time for the same portfolio? Previously There has been a number of posts on Value at Risk, including a basic introduction to Value at Risk and Expected Shortfall. The components garch model was also described. Issue The historical method for Value at Risk is by far the most commonly … Continue reading...

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The scaling of Expected Shortfall

June 16, 2013
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The scaling of Expected Shortfall

Getting Expected Shortfall given the standard deviation or Value at Risk. Previously There have been a few posts about Value at Risk and Expected Shortfall. Properties of the stable distribution were discussed. Scaling One way of thinking of Expected Shortfall is that it is just some number times the standard deviation, or some other number … Continue reading...

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Introduction to stable distributions for finance

June 10, 2013
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Introduction to stable distributions for finance

A few basics about the stable distribution. Previously “The distribution of financial returns made simple” satirized ideas about the statistical distribution of returns, including the stable distribution. Origin As “A tale of two returns” points out, the log return of a long period of time is the sum of the log returns of the shorter … Continue reading...

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Value at Risk and Expected Shortfall, and other upcoming events

June 4, 2013
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Value at Risk and Expected Shortfall, and other upcoming events

Highlighted Value at Risk and Expected Shortfall A two-day course exploring Value at Risk and Expected Shortfall, and their role in risk management. 2013 June 25 & 26, London. Lead by Patrick Burns. Details at the CFP Events site. New Events Thalesians — San Francisco 2013 June 5. Jesse Davis on “Risk Model Imposed Manager-to-Manager … Continue reading...

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Value at Risk with exponential smoothing

May 28, 2013
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Value at Risk with exponential smoothing

More accurate than historical, simpler than garch. Previously We’ve discussed exponential smoothing in “Exponential decay models”. The same portfolios were submitted to the same sort of analysis in “A look at historical Value at Risk”. Issue Markets experience volatility clustering.  As the previous post makes clear, historical VaR suffers dramatically from this.  An alternative is … Continue reading...

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Implied alpha and minimum variance

May 20, 2013
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Implied alpha and minimum variance

Under the covers of strange bedfellows. Previously The idea of implied alpha was introduced in “Implied alpha — almost wordless”. In a comment to that post Jeff noticed that the optimal portfolio given for the example is ever so close to the minimum variance portfolio.  That is because there is a problem with the example … Continue reading...

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Variance matrix differences

May 15, 2013
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Variance matrix differences

Torturing portfolios to give different volatilities between a factor model and Ledoit-Wolf shrinkage. Previously There have been posts on: “What the hell is a variance matrix?” factor models Ledoit-Wolf shrinkage Question Two of the several ways to produce an estimate of the variance matrix of asset returns is a statistical factor model and Ledoit-Wolf shrinkage.  … Continue reading...

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The half variance approximation for mean returns

May 6, 2013
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The half variance approximation for mean returns

What’s that thing about arithmetic and geometric returns and the variance? Previously An introduction to the difference between simple and log returns is: A tale of two returns Issue Suppose you are predicting the mean annual return of an asset for some number of years.  To simplify the discussion, let’s buy into the fantasy that … Continue reading...

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Slouching towards simulating investment skill

April 29, 2013
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Slouching towards simulating investment skill

When investment skill is simulated, it is often presented as if it is obvious how to do it.  Maybe I’m wrong, but I don’t think it’s obvious. Previously In “Simple tests of predicted returns” we saw that prediction quality need not look like what you would find in a textbook.  For example, there was a … Continue reading...

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