Open Thread: July 2010

komponisto

This thread is for the discussion of Less Wrong topics that have not appeared in recent posts. If a discussion gets unwieldy, celebrate by turning it into a top-level post.

Part 2

This thread is for the discussion of Less Wrong topics that have not appeared in recent posts. If a discussion gets unwieldy, celebrate by turning it into a top-level post.

Part 2

Your analogy is flawed, I think.

The weight of the rock pile is just what we call the sum of the weights of the rocks. It's just a definition; but the idea of general intelligence is more than a definition. If there were a real, biological thing called g, we would expect all kinds of abilities to be correlated. Intelligence would make you better at math and music and English. We would expect basically all cognitive abilities to be affected by g, because g is real -- it represents something like dendrite density, some actual intelligence-granting property.

People hypothesized that g is real because results of all kinds of cognitive tests are correlated. But what Shalizi showed is that you can generate the same correlations if you let test scores depend on three thousand uncorrelated abilities. You can get the same results as the IQ advocates even when absolutely no single factor determines different abilities.

Sure, your old g will correlate with multiple abilities -- hell, you could let g = "test score" and that would correlate with all the abilities -- but that would be meaningless. If size and location determine the price of a house, you don't declare that there is some factor that causes both large size and desirable location!

SarahC:

But what Shalizi showed is that you can generate the same correlations if you let test scores depend on three thousand uncorrelated abilities. You can get the same results as the IQ advocates even when absolutely no single factor determines different abilities.

Just to be clear, this is not an original idea by Shalizi, but the well known "sampling theory" of general intelligence first proposed by Godfrey Thomson almost a century ago. Shalizi states this very clearly in the post, and credits Thomson with the idea. However, for whatever ... (read more)

0[anonymous]16y

The way you define "real" properties, it seems you can't tell them from "unreal" ones by looking at correlations alone; we need causal intervention for that, a la Pearl. So until we invent tech for modifying dendrite density of living humans, or something like that, there's no practical difference between "real" g and "unreal" g and no point in making the distinction between them. In particular, their predictive power is the same. So, basically, your and Shalizi's demand for a causal factor is too strong. We can do with weaker tools.

4[anonymous]16y

"All of this, of course, is completely compatible with IQ having some ability, when plugged into a linear regression, to predict things like college grades or salaries or the odds of being arrested by age 30. (This predictive ability is vastly less than many people would lead you to believe [cf.], but I'm happy to give them that point for the sake of argument.) This would still be true if I introduced a broader mens sana in corpore sano score, which combined IQ tests, physical fitness tests, and (to really return to the classical roots of Western civilization) rated hot-or-not sexiness. Indeed, since all these things predict success in life (of one form or another), and are all more or less positively correlated, I would guess that MSICS scores would do an even better job than IQ scores. I could even attribute them all to a single factor, a (for arete), and start treating it as a real causal variable. By that point, however, I'd be doing something so obviously dumb that I'd be accused of unfair parody and arguing against caricatures and straw-men." This is the point here. There's a difference between coming up with linear combinations and positing real, physiological causes.