volatility, non-correlation …and beta

risk as volatility

Today is about volatility as a measure of risk.

It’s the standard academic method of assessment.  It has a certain initial intuitive plausibility.  After all, if your portfolio values is going all over the map, that sounds bad compared with one that just stays in one place.  Of course, the latter strategy is less damaging when there’s no inflation.  And there’s embedded just below the surface the efficient markets assumption that the highest possible return one can achieve is the market return.  The extra movement created by active management is not only occasionally scary, it just subtracts from your wealth.

you can’t spend risk-adjusted dollars

One of my old bosses used to say that you can’t spend risk-adjusted dollars.  What he meant is that higher volatility may be the price of achieving higher returns.  It doesn’t follow from this, other than in the ivory tower, that lower volatility/lower return investing is just as good.

Take the following two portfolios:

–one is trending upward at the rate of 15% annually, but at the end of any given month, can be as much as either 10% above or 10% below that trend

–the other is trending upward at the rate of 10% annually, but at the end of any given month can be as much as either 3% above or 3% below the trend.

At the end of ten years, the first portfolio is up by 300%, +/- 10%.

The second is up by 160%, +/- 3%.

Try explaining to the second client that he’s just as well off as the first.

why use volatility

Why use volatility as a measure, then?

The main reason, I think, is that data are easily available for computers, so volatility has the feel of being objective.  Another is the semi-religious belief that outperformance is impossible, in which case having extra volatility is an undiluted negative.  (By the way, having a portfolio that outperforms the market day after day, month after month, in an up market is, by definition, more volatile than an index fund.)


For someone who needs the money tomorrow, or next week or next month, a long-term investment with short-term volatility is the last place we want money to be.

Older investors, who are using savings to live on, have got to have a substantial cash reserve to avoid having to sell potentially volatile holdings during a -10% phase.

And a portfolio that consistently produces low returns coupled with high volatility has trouble written all over it.

more on risk as volatility

volatility as risk

I was listening to Bloomberg radio the other day when a talking head who usually has interesting things to say (an increasing rarity on Bloomberg) began to “explain” how 2015 was a very risky year for stocks.  This, even though the S&P 500 was ending December in basically in the same place it started out in January.

Measures of interday change in individual stock prices were also relatively benign   …but, he said, intraday price movements in stocks were unusually high.  Therefore, stocks were riskier than usual.

Yes, in a very tortured sense…or for a day trader who’s consumed by hour-to-hour price movements…that might be so.  For you and me, though, that’s crazy.


Last September 14th I wrote another post about the academic notion that investment risk can be defined as day-to-day volatility, i.e., the daily change in the price of a given security.

The main pluses for this idea are that it’s simple, the data are readily available and you don’t have to know anything about the security in question or the goals of the holder.

In my earlier post, I pointed out that this notion led to catastrophic results in the late 1980s-early 1990s for institutional holders of commercial real estate and junk bonds.  Neither traded very often, so the daily price–as determined by the last actual transaction–rarely changed. Volatility was negligible.  What a surprise when lots of people wanted to sell at the some time, only to find that low volatility didn’t represent safety.  It signaled illiquidity–there were no buyers at anywhere near the last trade.

not a 100% useless concept

There is a sense in which volatility may be important, though.  Over several year periods, stocks tend to follow an up and down pattern that mirrors the business cycle, with stocks leading the economy by about six months.  Over longer periods, stocks tend to advance on trend around the rate of growth in reported profits, which has historically been about +8% per year in the US.


If you’re in your thirties or forties and saving for your retirement or to pay for your young children’s college tuition, then daily or even business cycle fluctuations in stock prices are irrelevant now.  Investing in stocks that have low volatility–which usually also comes with low appreciation potential–makes no sense at all, despite the notion’s academic pedigree.

On the other hand, if you’re saving, say, for a wedding or to buy a house and will need the funds in six months or a year, then having it in stocks is probably a bad idea.  That’s because prices could easily be 10% below today’s level when you need the money.  Just look at a chart of the S&P 500 in 2015–which chronicles a mid-summer S&P swoon– to see what I mean.  In this case, keeping your money in (low-volatility) cash is the better course of action.





risk and volatility


I think that defining what risk is is the most difficult topic in finance/investing.

I’m not sure there’s one answer that fits everyone and everything.

We do know that individuals’ perception of what risk entails changes as they age or as their wealth increases; they become more conservative.  We also know that appearances can be deceiving.  A model with a perfectly proportioned body may be clumsy or a terrible athlete.  Experience counts for something, as well.  Situations that appear risky when a neophyte is in control, like in doing brain surgery, may in fact be relatively safe in the hands of an expert.  Information is important, too, like having enough data or experience to know who is the beginner and who is the well-trained seasoned pro.

risk as volatility

Academic finance, and following its lead, pension consultants and their pension fund clients, have all chosen to reduce this complexity to a single concept, risk = volatility.  In other words, the magnitude of day to day price changes in securities. This can be expressed either in absolute form or relative to some benchmark, and may be measured over differing time periods.

Defining risk as volatility has three big advantages:

–easy data availability

–quantitative form


In a world where no one runs with scissors or texts while driving, or where there’s never a flood, a tornado or huge food items falling from the sky (like in Chewandswallow), that would be enough.

In practice, however, volatility isn’t such a hot measure.

On a very abstract level, there’s no recognition of the issue that philosophers have been pondering for the past two centuries or so–that groups may not be connected by every member having a single thing in common.  One alternative is the possibility of “family resemblances” popularized by Ludwig Wittgenstein over a half-century ago.  So maybe there isn’t one common factor that constitutes risk.

On a more practical level, in the real world not everyone has the same information.  History also shows that markets periodically become highly emotional, either wildly optimistic or deeply pessimistic.  My conclusion, based on decades of experience, is that the results of daily trading don’t constitute infallible indicators.  Quite the opposite–most often one should take the evidence of daily trading with a grain of salt.

…but does it trade?

To my mind, though, the most striking failure of volatility as a risk measure is that it doesn’t take liquidity into account.

An example of what I mean:

In the mid 1980s, I came across for the first time academic articles that touted real estate as the most attractive of major asset classes.

How so?

The argument was that since the end of WWII real estate had not only a higher annual rate of return than stocks or bonds, but it also had the lowest average price volatility of the three.  Not only did real estate deliver the highest absolute gains, but adjusting for its low “risk” property ownership looked even better.  This was an odd result, because one typically thinks that reward and risk are directly correlated, not inversely.  But no one questioned it.

real estate

Anyone who has owned a home over an extended period of time, to say nothing of owners of commercial or office real estate, knows this is loony.  In bad times, bank finance disappears and, along with this, so too transactions.  During 1981-83 in the US, when I experienced this phenomenon first-hand, houses could only be sold at extremely steep discounts to pre-recession prices–or to owners’ notions of fair value based on rental equivalents.  Potential buyers made very low-ball offers, prospective sellers took their homes off the market, and no transactions happened.  In the very narrow sense, therefore, volatility was low.  But that was because there were no sales to demonstrate how the market had deteriorated, prices were stable.  You just couldn’t sell.

junk bonds

The collapse of the junk bond market in the late 1980s demonstrated the same idea.  Junk bonds had been touted as having “all the rewards of stocks with all of the safety of bonds.”  The safety part proved an illusion.  The apparent stability of the net asset values of junk bond funds ended up resting in large part on the fact that the bonds they held seldom traded.  So every day the funds priced themselves using more or less the last trade, which might have been weeks ago–and which might not reflect current circumstances.  This idyll lasted until funds began to have net redemptions, forcing them to sell bonds at real market prices, which were often way below their carrying value on  fund books.