Are financial speculations really "harmful human activities"?

It is worrisome when not one but two eminent economists denounced financial speculation as "harmful human activities" in the short space of 2 weeks. (See Paul Krugman's column here and Robert Frank's here.) It is more worrisome when their proposed cure to this evil is to apply a financial transaction tax to all financial transactions.

Granted, you can always find this or that situation when financial speculation did cause harm. Maybe speculation did cause the housing bubble. Maybe speculation did cause an energy price bubble. In the same vein, you can also argue that driving is a harmful human activity because cars did cause a few horrific traffic accidents.

No, we can't focus on a few catastrophes if we were to argue that financial speculation is harmful. We have to focus on whether it is harmful on average. And on this point, I haven't seen our eminent economists present any scientific evidence. On the other hand, as an ex-physicist and an Einstein-devotee, I can imagine some  thought experiments (or gedankenexperiment as Einstein would call them), where I can illustrate how the absence of financial speculation can clearly be detrimental to the interests of the much-beloved long-term investors. To make a point, a gedankenexperiment is usually constructed so that the conditions are extreme and unrealistic. So here I will assume that the financial transaction tax is so onerous that no hedge funds and other short-term traders exist anymore.

Gedankenexperiment A: Ms. Smith just received a bonus from her job and would like to buy one of her favorite stocks in her retirement account. Unfortunately, on the day she placed her order, a major mutual fund was rebalancing its portfolio and had also decided to shift assets into that stock. In the absence of hedge funds and other speculators selling or even shorting this stock, the price of that stock went up 40% from the day before. Not knowing that the cause of this spike was a temporary liquidity squeeze, and afraid that she would have to pay even more in the future, Ms. Smith paid the ask price and bought the stock that day. A week later, the stock price fell 45% from the peak after the mutual fund buying subsided. Ms. Smith was mortified.

Gedankenexperiment B: Mr. Smith decided that the stock market is much too volatile (due to the lack of speculators!) and opted to invest his savings into mutual funds instead. He took a look at his favorite mutual fund's performance, and unfortunately, its recent performance seemed to be quite a few notches below its historical average. The fund manager explained on her website that since her fund derived its superior performance from rapidly liquidating holdings in companies that announced poor earnings, the absence of liquidity in the stock market often forced her to sell into an abyss. Disgusted, Mr. Smith opted to keep his savings in his savings account.

Of course, our economists will say that the tax is not so onerous that it will deprive the market of all speculators (only the bad ones!?). But has anyone studied if we impose 1 unit of tax, how many units of liquidity in the marketplace will be drained, and in turn, how many additional units of transaction costs (which include implicit costs due to the increased volatility of securities) would be borne by an average investor, who may not have the luxury of submitting a limit order and waiting for the order to be filled?

Picking up nickels in front of steamrollers

When I was growing up in the trading world, high Sharpe ratio was the holy grail. People kept forgetting the possibility of "black swan" events, only recently popularized by Nassim Taleb, which can wipe out years of steady gains in one disastrous stroke. (For a fascinating interview of Taleb by the famous Malcolm Gladwell, see this old New Yorker article. It includes a contrast with Victor Niederhoffer's trading style, plus a rare close-up view of the painful daily operations of Taleb's hedge fund.)

Now, however, the pendulum seems to have swung a little too far in the other direction. Whenever I mention a high Sharpe-ratio strategy to some experienced investor, I am often confronted with dark musings of "picking up nickels in front of steamrollers", as if all high Sharpe-ratio strategies consist of shorting out-of-the-money call options.

But many high Sharpe-ratio strategies are not akin to shorting out-of-the-money calls. My favorite example is that of short-term mean-reverting strategies. These strategies not only provide consistent small gains under normal market conditions, but in contrast to shorting calls, they make out-size gains especially when disasters struck. Indeed, they give us the best of both worlds. (Proof? Just backtest any short-term mean-reverting strategies over 2008 data.) How can that be?

There are multiple reasons why short-term mean-reverting strategies have such delightful properties:

1. Typically, we enter into positions only after the disaster has struck, not before.
   
2. If you believe a certain market is mean-reverting, and your strategy buy low and sell high, then of course you will make much more money when the market is abnormally depressed.
3. Even in the rare occasion when the market does not mean-revert after a disaster, the market is unlikely to go down much further during the short time period when we are holding the position.

"Short-term" is indeed the key to the success of these strategies. In contrast to the LTCM debacle, where they would keep piling on to a losing position day after day hoping it would mean-revert some day, short-term traders liquidate their positions at the end of a fixed time period, whether they win or lose. This greatly limits the possibility of ruin and leaves our equity intact to fight another day in the statistical game.

So, call me old-fashioned, but I still love high Sharpe-ratio strategies.

In praise of ETF's

I have learned some years ago that ETF's are strange and wonderful creatures. Simple, long-only mean-reverting strategies that work very well on ETF's, won't work on their component stocks. (Check out a nice collection of these strategies in Larry Connors' book "High Probability ETF Trading". He has also packaged these strategies into a single indicator, the ETF Power Ratings, on tradingmarkets.com.) Simple pair trading strategies like the one I discussed in my book, also work much more poorly on stocks than on ETF's. Why is that?

Well, one obvious reason is that, as Larry mentioned in his book, ETF's are not likely to go bankrupt (with the notable exception of the triple-leveraged ETF's, as I explained previously), because a whole sector or country is not likely to go bankrupt. So you can pretty much count on mean-reversion if you are on the long side.

Another obvious reason is that though there are news which will affect the valuation of a whole sector or country, these aren't as frequent or as devastating as news affecting individual stocks. And believe me, news is the biggest enemy of mean-reversion.

But finally, I believe that the capital weightings of the component stocks also play a part in promoting mean-reversion. Typically, weighting of a component stock increases with its market capitalization, though not necessarily linearly. Perhaps large-cap stocks are more prone to mean-reversion than small-cap stocks? But more intriguingly, can we not construct a basket of stocks, with custom-designed weightings, with the objective of optimizing its short-term mean-reversion property? I (and others before me) have done something similar in constructing a basket of stocks that cointegrate best with an index. Can we not construct a basket that is simply stationary (with perhaps a constant drift)?

Now, perhaps you will agree with me that ETF's are strange and wonderful creatures.