I found a description of it. It is just another way of using overbought-oversold. I suspect it will work, just as some others such as RS2, Bol Bands, fib or percentage levels, etc. But how well they work and how to handle them when the market is dropping and dropping and dropping...that is the question!
This unique unilateral pair trading system is disclosed by James Altucher in his book, "Trade Like a Hedge Fund," Wiley (2002). Normally pairs trading implies a market neutral strategy where one goes long one asset and short the other. In the author's words: "The key difference in using unilateral pairs trading is that we will not trade both sides of the spread, but the side that is historically more volatile. The idea is that the more volatile side is most often the culprit for why the spread has gone awry. For this reason we will treat QQQ and SPY as a pair, but we will trade only QQQ." The stated trading rules are:
1. Calculate the ratio of the QQQ price series over the SPY price series.
2. Calculate the 20-day moving average of that ratio.
3. For each day, calculate the difference between the ratio and its moving average.
4. Calculate the 20-day moving average of those differences.
5 For each day, calculate how many standard deviations the difference in ratios is for that day from its moving average. Calculate the standard deviation for each day using its prior 20 days.
6. For each day, if the standard deviation calculated is greater than 1.5 and QQQ is 2 percent greater that the prior day, then short QQQ.
7. For each day, if the standard deviation calculated is less than -1.5 and QQQ is 2 percent lower than the prior day, then buy QQQ.
8. Sell/cover when the standard deviation of the difference in the ratios is less than 0.5 (in the case of a short) or greater than -0.5 (in the case of a long).