# Blog Archives

## Random portfolios versus Monte Carlo

July 2, 2012
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What is the difference between Monte Carlo — as it is usually defined in finance — and random portfolios? The meaning of “Monte Carlo” The idea of “Monte Carlo” is very simple.  It is a fancy word for “simulation”. As usual, it is all too possible to find incredibly muddied explanations of such a simple … Continue reading...

## Two new, important books on R

June 22, 2012
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Two books were recently published that are sure to help R grow even faster. R has a reputation, partially deserved, for being hard to learn.  These books will help.  The first makes learning easier, the second can make learning less necessary for initiates. I have not yet touched either book. R for Dummies The authors … Continue reading...

## To R or not to R, and other events

June 21, 2012
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New events To R, or not to R, that is the question The Statistical Computing Section of the Royal Statistical Society presents a one-day event on 2012 June 29. The details of the day.  See in particular the abstract for “Teaching statistics: a pain in the R?” by Andy Field — it involves a sheepdog … Continue reading...

## Cross sectional spread of stock returns

June 18, 2012
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A look at a simplistic measure of stock-picking opportunity. Motivation The interquartile range (the spread of the middle half of the data) has recently been added to the market portrait plots.  Putting those numbers into historical context was the original impulse. However, this led to thinking about change in stock-picking opportunity over time. Data Daily … Continue reading...

## Variability in maximum drawdown

June 4, 2012
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Maximum drawdown is blazingly variable. Psychology Probably the most salient feature that an investor notices is the amount lost since the peak: that is, the maximum drawdown. Just because drawdown is noticeable doesn’t mean it is best to notice. Statistics The paper “About the statistics of the maximum drawdown in financial time series” explores drawdown … Continue reading...

## Inferno-ish R

May 31, 2012
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CambR was nice enough to invite Markus Gesmann and me to speak at their event on Tuesday. My talk was Inferno-ish R. See also The R Inferno. Epilogue Subscribe to the Portfolio Probe blog by Email

## Jackknifing portfolio decision returns

May 28, 2012
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A look at return variability for portfolio changes. The problem Suppose we make some change to our portfolio.  At a later date we can see if that change was good or bad for the portfolio return.  Say, for instance, that it helped by 16 basis points.  How do we properly account for variability in that … Continue reading...

## Correlations and postive-definiteness

May 22, 2012
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On the way to another destination, I found some curious behavior with average correlations. The data Daily log returns from almost all of the constituents of the S&P 500 for years 2006 through 2011. The behavior Figure 1 shows the actual mean correlation among stocks for the set of years and the mean correlation with … Continue reading...

## CambR and other upcoming events

May 21, 2012
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New events CambR (Cambridge UK R user group) 2012 May 29 6:30 PM for 7:00 PM start. Pat Burns “Inferno-ish R” Abstract: While R is wonderful, it is not uniformly wonderful. We highlight a few things generally found to be confusing, and outline the forces that have driven such imperfections. Markus Gesmann “Interactive charts with … Continue reading...

## Exponential decay models

May 17, 2012
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All models are wrong, some models are more wrong than others. The streetlight model Exponential decay models are quite common.  But why? One reason a model might be popular is that it contains a reasonable approximation to the mechanism that generates the data.  That is seriously unlikely in this case. When it is dark and … Continue reading...