I am currently reading Dr. Richard Haier's book The Neuroscience of Intelligence and I am a little confused about the g-factor. Note that I have no education in psychology outside of general ed courses at university.
I have two questions regarding the g-factor. What confuses me is for one, he does not go into technical detail about how the g-factor is calculated.
He does include this illustration:
Here we see that 15 mental tests are taken in groups of 3, where each group is correlated to a certain factor. So tests 1-3 are for reasoning, 4-6 for spatial ability, and so on. These factors then correlate to the g-factor.
I am wondering what is the methodology used to find the correlations between the tests and factors/factors and the g-factor? For example, I don't quite understand how they measure the correlation between the test and the factor given that the factor is abstract (ie. reasoning). I hope what I am asking makes sense. I am not asking how to perform linear regression or calculate Pearson's r.
My second question is about the statement in the book:
"Different mental abilities are not independent. They are all related to each other and the correlations among mental tests are always positive.... It strongly implies that all the factors derived from individual tests have something in common, and this common factor is called the general factor of intelligence."
Wouldn't this imply that all of the factors are multicollinear and make it difficult to distinguish which factors are most significant?