Using Historical Averages Can Make You Money In Stocks

A concept that I’ve explored lately in this recent volatile market is reversion to the mean, which suggests that prices have a tendency of eventually moving back towards their long-term historic averages.

A good example of this could be the price of oil. After rising 47% in the first half 2008 and hitting a record high of $147 per barrel on July 11, the price of oil has dropped more than 20% in less than eight weeks as supply-demand dynamics adjusted (Not including the speculative bounce last week). Albeit $120 oil can still be considered high by historical standards, the point is that dramatic increases over short periods of time represent imbalances that are likely to self-correct.

Using The Reversion Theory In Your Portfolio

Within the context of recent history, many people might associate reversion with a downward movement so the first thing that comes to mind is something that’s overpriced. However, if we turn this concept over in order to highlight value as well. For example, while oil has soared to new heights, at the other end of the spectrum global equities have been punished and U.S. stocks in particular have struggled amid the credit crunch and a deteriorating economic backdrop.

Over the last 12 months, the return on the S&P 500 Index has been about -11%. Consider however that the average annual return on U.S equities over the past 25 years is 11.4%. On this basis, investors (especially those sitting on the sidelines in cash) might want to ask themselves whether they think stock prices in the world’s largest and most diverse economy will stay at current levels indefinitely, or whether it’s more reasonable to think that at some point, they’ll revert to more historically normal levels.

Analysts spend many hours and a boat-load of money determining what they perceive as fair value for equity markets. Their valuation models incorporate long run averages for inflation, interest rates and growth and based on current levels for these factors, U.S. equities appear to be trading below fair value. Another way to interpret the reversion theory essentially is a version of the “stocks on sale” message.

Reverting To Positive Returns

If U.S. equities are trading below where they should be based on historic averages for similar environments, then it follows that at some point, they should move back towards fair value, meaning stock prices should eventually rise.

Now, I am NOT forecasting what the price of oil will be or where U.S. stocks will be trading six months from now or when reversion will happen – I’ll leave that to the “experts” . The message to take from this is that amid 200 point swings in the stock market or $10 spikes in oil prices, it’s prudent to think about where prices are in relation to historic long run averages.

In a volatile market it becomes very difficult to predict which individual stocks are going to be most successful. However, buying a broad index such as the S&P 500 will offer significant exposure to a US equity market that has become oversold and is valued at well below historical averages. Not to mention that the S&P 500 has a dividend growth rate of about 11%. So, buying this index offers you an average of 11% raise each year while we wait for valuations to return to the mean.


  1. I’ve stumbled across a similar perspective.

    If one looks at a 5 yr Weekly chart with 10 week and 40 week moving averages on an index like the $SPX one can see the continual “touches” back to the 40 week moving average.

    When the market swings past its 10 week average and then drags that 10 week past the 40 week, then and only then do we have a trend change.

    At the moment … we’re going down and we’ll continue to go that way.

  2. DM: I use something similar. For entry point, I look at the distance of existing stock price from moving averages (26w and 52w). It just give me a better entry point. e.g. I waited close of one year for jnj to get a good entry point. I would have not covered the difference with one year worth of dividend…

  3. DT,
    It takes a lot of patience to wait one year for an entry point. However, your future returns are drastically affected by your initial purchase price – many people do not have the patience to wait for their entry point.

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