In the context of an attack on Howard Gardner’s theory of multiple intelligences (10 page PDF), David F. Lohman (of the University of Iowa) presents this visualization of the hierarchies of intelligence tests:
The closer to the center, the more general lintelligence (“g”) loads on the test. Some tests, such as identifying the correct endings of words, reading speed, or listening comprehension test “g” more indirectly than measures of verbal achievement, paper folding, or necessary arithemetic operations.
A good example is the Test Necessary Arithmetic Operations. This test was devised by Guilford to measure a specific cell in his Structure of the Intellect Model. Each item presents a short word problem. The examinee’s task is not to solve the problem, but to say which two operations she would use, and in what order. There are four operations: add, subtract, multiply, and divide. Thus, problems do not require advanced mathematics. Yet in the sample of over 100 Stanford undergraduates who were administered most of the tests in Figure 2, Necessary Arithmetic Operations had one of the highest loadings on the [fluid intelligence] factor (Marshalek, Lohman, & Snow, 1983).
I meant this because of Mark’s discussion of Dr. James Flynn on the Flynn Effect. Essentially, the Flynn effect explains the large-scale increase in measured general intelligence over the 20th century as reflecting increased society-wide patterns of practice on subtests. This implies two things: first, that tests should be renormalized every so often to make sure they still measure “g,” and not practice. Second, that ability improves with practice.
It strikes me that, when properly normalized, IQ measures something psychobioneurological… perhaps not working memory exactly, but something not too far apart from that concept.
This has implications for the heritability of IQ. Most obviously, the more environment changes, the more change in performance can be traced to the environment. (Of course, as environments become more similar, more of the variation in the population will be explained by environments.)