Skip to main content

Stock Prices and Alpha




Aside from the considerations we discussed last week, there is this to remember about stock performance, the performance of a stock as an investment is not (entirely) a matter of whether it rises or falls in price. A stock also entitles its holder to a portion of whatever dividends the issuing company may declare. Suppose, then, that we do the arithmetical magic to factor in the dividend stream as if it were being paid out day by day, and we included that along with the stock price move as the performance of XYZ. Once we do this, we’ll want to be sure that we’re matching the stock price against a broad market benchmark that also includes dividends as part of performance.

Fortunately, these are readily available. The S&P Index, for example, comes in three variants: one that considers solely the price of component stocks; one that factors in dividends (the “total return” index); and a third that subtracts the tax on those dividends (“net return.”)

We might make discussion easier by giving a name to the difference between the stock performance figure for a particular stock (or of your personal portfolio of stocks) on the one hand, and of the broad market’s equivalent on the other. Let us call this difference alpha.

Positive alpha is a good thing. It means you're doing better than 'the house.' Negative alpha means you're doing worse.

Now: a curve for a particular stock’s alpha as we’ve defined it will often look a lot like the Bell curve. One significant implication of this: alpha nets out to zero. That is worth saying again: alpha nets out to zero. In graphical terms, there is as much space beneath the left-hand (negative alpha) side of the pertinent bell curve as there is beneath the right-hand (positive alpha) side of the curve.

This is a good moment to observe that stock picking, betting your nest egg on the future of individual stocks, or on some expensive “active manager's” ability to buy individual stocks, is usually a bad idea. It is cheaper and safer to invest indirectly through broad based (passively managed) funds or exchange traded funds (ETFs).  It is best to bet on that index against which alpha is measured, rather than betting on some stock’s alpha itself.  Why? Because (a) have I mentioned this yet? alpha nets out to zero and (b) if you're trying to beat the market, you're paying a broker and/or advisers for that zero.

Let us ask another sort of question now. If stock price moves are random (or to the extent that they are): why are they random?

One widespread view is that stock prices jump about in a “random walk” fashion precisely because the stock market is accomplishing its job. This is also, with important qualifications, my own view: the market is a venue for the efficient allocation of capital, according to rational expectations, and the randomness arises from that fact. This is a somewhat counter-intuitive idea. After all, in most contexts in our day-to-day life randomness is a bad thing. When I get up in the morning and get into my car for the drive to work and turn the key in the ignition, I want the car to start. Deterministically. Certainly. I don’t want there to be any uncertainty or randomness about it!

But the stock markets are a rather different sort of mechanism. Or, rather, they aren’t a sort of mechanism at all, but a meeting place for a lot of different vitalisms. And in this context, it might help us to consider a simple seasonal development, like the arrival of Halloween. Presumably in parts of the world where Halloween is celebrated, the demand for pumpkins rises rather suddenly every October and falls even more suddenly at the end of that month.
“Aha!” says the naïve investor, “so I can get rich! All I have to do is find a way to bet all my money and all the money I can borrow on the prospect that pumpkins will rise in price this coming October. My bet will pay off, and I’ll be rolling in enough dough to take full advantage of the big cranberry crunch the following month.”
Sorry, that doesn’t work. If you voice such a speculation out loud, your neighbor surely says, “if it were that easy, everyone would do it.” And he’s right. Think of the market as a collective intelligence: Mr. Market. Now, surely, Mr. Market knows that people are going to want to buy pumpkins by late October and are going to want cranberries by late November. The prices of these products and all derivatives of those prices factor in such matters. So, sorry, you don’t get to outsmart Mr. Market that way.

Comments

Popular posts from this blog

A Story About Coleridge

This is a quote from a memoir by Dorothy Wordsworth, reflecting on a trip she took with two famous poets, her brother, William Wordsworth, and their similarly gifted companion, Samuel Taylor Coleridge.   We sat upon a bench, placed for the sake of one of these views, whence we looked down upon the waterfall, and over the open country ... A lady and gentleman, more expeditious tourists than ourselves, came to the spot; they left us at the seat, and we found them again at another station above the Falls. Coleridge, who is always good-natured enough to enter into conversation with anybody whom he meets in his way, began to talk with the gentleman, who observed that it was a majestic waterfall. Coleridge was delighted with the accuracy of the epithet, particularly as he had been settling in his own mind the precise meaning of the words grand, majestic, sublime, etc., and had discussed the subject with William at some length the day before. “Yes, sir,” says Coleridge, “it is a majesti

Five Lessons from the Allegory of the Cave

  Please correct me if there are others. But it seems to be there are five lessons the reader is meant to draw from the story about the cave.   First, Plato  is working to devalue what we would call empiricism. He is saying that keeping track of the shadows on the cave wall, trying to make sense of what you see there, will NOT get you to wisdom. Second, Plato is contending that reality comes in levels. The shadows on the wall are illusions. The solid objects being passed around behind my back are more real than their shadows are. BUT … the world outside the the cave is more real than that — and the sun by which that world is illuminated is the top of the hierarchy. So there isn’t a binary choice of real/unreal. There are levels. Third, he equates realness with knowability.  I  only have opinions about the shadows. Could I turn around, I could have at least the glimmerings of knowledge. Could I get outside the cave, I would really Know. Fourth, the parable assigns a task to philosophers

Searle: The Chinese Room

John Searle has become the object of accusations of improper conduct. These accusations even have some people in the world of academic philosophy saying that instructors in that world should try to avoid teaching Searle's views. That is an odd contention, and has given rise to heated exchanges in certain corners of the blogosphere.  At Leiter Reports, I encountered a comment from someone describing himself as "grad student drop out." GSDO said: " This is a side question (and not at all an attempt to answer the question BL posed): How important is John Searle's work? Are people still working on speech act theory or is that just another dead end in the history of 20th century philosophy? My impression is that his reputation is somewhat inflated from all of his speaking engagements and NYRoB reviews. The Chinese room argument is a classic, but is there much more to his work than that?" I took it upon myself to answer that on LR. But here I'll tak