Similar evidence appeared in songbirds and rats around the same time, and since then, researchers have built up an impressive catalogue of animal lateralisation.
You no longer have to worry about picking the correct one, as the tool is smart enough to determine which one you want based on UML rules and common sense.
It's no longer enough to show, for example, that parents who are conscientious about child rearing tend to have children who are conscientious about their schoolwork.
So what Kennedy was referring to was that while GDP has been the most common method for measuring the economic activity of nations, as a measure, it is no longer enough.