The process of doing so is not as straightforward as it sounds, because something might simultaneously explain both air-traffic and growth, and so it is necessary to go through a complicated econometric procedure to purge any correlation of air traffic and growth of variables that might explain both.
"You potentially have a bomb above your head and then you have sea landings and landings at night with power cables so it's not a straightforward thing, " he said.
Notso long ago, investors would be well-served to build a simple, straightforward portfolio consisting primarily of U.S.-based multinational stocks and high quality U.S. municipal bonds.