Here the situation is different in that it’s not just that we don’t know how to measure X, but rather the way in which we have derived X means that directly measuring it is impossible even in principle.
That’s distinct from something like (say) self-esteem, where it might be the case that we might figure out what self-esteem really means, or at least come up with a satisfactory instrumental definition for it. There’s nothing in the normal definition of self-esteem that would make it impossible to measure on an individual level. Not so with g.
Of course, one could come up with a definition for something like “intelligence”, and then try to measure that directly—which is what people often do, when they say that “intelligence is what intelligence tests measure”. But that’s not the same as measuring g.
This matters because it’s part of what makes e.g. the Flynn effect so hard to interpret—yes raw test scores on IQ tests have gone up, but have people actually gotten smarter? We can’t directly measure g, so a rise alone doesn’t yet tell us anything. On the other hand, if people’s scores on a test of self-esteem went up over time, then it would be much more straightforward to assume that people’s self-esteem has probably actually gone up.
Here the situation is different in that it’s not just that we don’t know how to measure X, but rather the way in which we have derived X means that directly measuring it is impossible even in principle.
That’s distinct from something like (say) self-esteem, where it might be the case that we might figure out what self-esteem really means, or at least come up with a satisfactory instrumental definition for it. There’s nothing in the normal definition of self-esteem that would make it impossible to measure on an individual level. Not so with g.
Of course, one could come up with a definition for something like “intelligence”, and then try to measure that directly—which is what people often do, when they say that “intelligence is what intelligence tests measure”. But that’s not the same as measuring g.
This matters because it’s part of what makes e.g. the Flynn effect so hard to interpret—yes raw test scores on IQ tests have gone up, but have people actually gotten smarter? We can’t directly measure g, so a rise alone doesn’t yet tell us anything. On the other hand, if people’s scores on a test of self-esteem went up over time, then it would be much more straightforward to assume that people’s self-esteem has probably actually gone up.