reversion to the mean

Mean version has two senses:

1.  The first is important for traders, less so for investors.  It’s that if we construct a trend line or moving average for a stock from past prices, the stock will tend to trade in a reasonably well-defined band or channel around the trend.  In theory at least, one can make money by buying when the stock is at the lower edge of the band and selling when it’s at the higher edge.

2.  The second is a cardinal tenet for value investors.  It’s that over long periods of time stocks in general tend to rise and fall in line with overall earnings performance, which is, in turn, a function of the ebb and flow of nominal GDP.  Some stocks may have episodes where they perform far better than that.  Others may have extended periods when they fall far short of this mark, which in the US probably averages around +8% per year.  The value investor’s argument is that both classes, serial outperformers and serial underperformers alike, will inevitably see their fortunes reverse and their stocks revert to the long-term mean performance.

For high-fliers, this means they’ll, sooner or later, crash and burn.  For the stock market’s junk pile, on the other hand, its denizens will have periods when they’ll rise like the phoenix.  The latter are what value investors look for.

old school value investing

For some value investors, this is it.  This is all they do.  They run screens that find the cheapest stocks based on price/cash flow, price/earnings or price/assets–or some combination of the three.  And then they buy them.

I knew one who systematically went through books of charts looking for stocks that had experienced catastrophic drops (not a good strategy–once they figured out what he was doing, brokers began to send this guy charts with the price axis stretched out and the time axis compressed, so that every stock they touted looked like a train wreck.  Last I heard–I was hired to clean up the unholy mess he created–he was selling real estate in the Philippines).

Every investor is in some sense a contrarian.  At the very least, we all believe that the stock we are buying has more up left in it than the seller does, and the stock we are selling has less.  We also know the cardinal rule is to “buy low and sell high.”  Nevertheless, I think the simple strategy I just outlined, which is at the heart of the value investing practiced a generation ago, no longer works.

Why am I writing about this today?  

I was listening to Bloomberg radio in my car yesterday,when Dave Wilson repeated the observation of a market strategist that the divergence between the strong relative performance of the sector ETF for Consumer Discretionary and the weak outcome for Staples was as great as it was just before the Internet bubble popped in 2000.  What followed was a fierce reversion to the mean by both sectors.

The implication was that this factoid is significant.  As usual for Bloomberg, what or why was not forthcoming.

More tomorrow.



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