The key factor when comparing the two legs would be statistical fitness.
In addition to a high degree of positive statisitical relationship between spread legs, traditional spread traders also usually demand a high degree of positive fundamental relationship between the legs. An example would be a US Treasury Bill versus a similar duration Eurodollar future, Nymex Heating Oil versus Nymex Crude Oil, or equity shares within the same market sector and with similar market caps: IBM vs HPQ or WMT vs TGT would be an example.
Stat Arb traders are typically concerned primarily with the statistical relationship between spread leg combinations - remember, the idea is to capture arbitrage differences between highly correlated instruments and insulate yourself from broad market delta directionality in the process. One example is HOG vs. ENS: Harley Davidson (motorcycles) versus Enersys (industrial lighting); both have a positive correlation of 95.7% over the past two years daily close-on close. Obviously, both companies have next to nothing in common otherwise. The quants are updating their databases every day before the open.
In addition to a high degree of positive statisitical relationship between spread legs, traditional spread traders also usually demand a high degree of positive fundamental relationship between the legs. An example would be a US Treasury Bill versus a similar duration Eurodollar future, Nymex Heating Oil versus Nymex Crude Oil, or equity shares within the same market sector and with similar market caps: IBM vs HPQ or WMT vs TGT would be an example.
Stat Arb traders are typically concerned primarily with the statistical relationship between spread leg combinations - remember, the idea is to capture arbitrage differences between highly correlated instruments and insulate yourself from broad market delta directionality in the process. One example is HOG vs. ENS: Harley Davidson (motorcycles) versus Enersys (industrial lighting); both have a positive correlation of 95.7% over the past two years daily close-on close. Obviously, both companies have next to nothing in common otherwise. The quants are updating their databases every day before the open.
