[david927]

valid measure ... some predictive power

I'm not sure if those two belong in the same sentence. If we were to come up with a point system that measured beauty in women, for example, you could measure pronouncement of cheekbones and thickness of lips, etc. While Angelina Jolie would score well, so would Jocelyn Wildenstein, and Emma Watson would score poorly. Such a system might have "some predictive power" for large population sizes, but could never measure "beauty".

Intelligence is qualitative, like beauty, not quantitative, and therefore could never be expressed individually as a number. We would do well to bear that in mind.