Quote from jones247:
When pair trading two stocks (preferably within the same sector), there's a MAJOR PROBLEM with the mean-reversion strategy. The assumption is that the two stocks will converge after diverging to a certain point. Oftentimes, layering-in is used to improve the performance of the mean-reversion plan (i.e. "it did not revert on the 1st entry, let's try to enter again - hoping that the reversion will occur after the next std deviation).
This is the crux of the problem: If fundamentals dictate that you long the strong stock and short the weaker stock, then one would think that the stock is more likely to continue to diverge rather than converge. To bet on a mean-reversion, one would typically need to short the strong stock and long the weak stock. In doing so, it appears that you're betting against market fundamentals.
In a nutshell, my theory is that it may be better to trade with the trend of the divergence than to try and anticipate a reversal (mean reversion) of the two stocks. In other words, once a pair start to diverge (especially if supported by fundamentals such as earnings or news reports), then enter the spread with the plan of the divergence continuing.
Perhaps mean-reversion would be better suited with indicies, such as the spy vs. dia...
your thoughts... Do you see a problem with my logic???