Income, Intelligence and Inequality

Abstract

The Factor The Science of Mental Ability Arthur R. Jensen Praeger, 1998 As readers of this journal will know, the g is the term used by psychometricians to designate what is popularly called Author Arthur Jensen is arguably the world's leading expert on intelligence (over 300 papers published) and this book summarizes his life's work. This makes it a major work and one that will be used for years. Jensen argues that the tests of mental ability reflect heavily a single factor, usually abbreviated g, and that this corresponds closely to what we call intelligence. By being very precise about what is being talked about, some of the semantic difficulties raised by those who don't want to admit that people differ in thinking power are avoided. Unfortunately there are difficulties for the non-mathematician in even understanding what factor analysis is, or exactly what is. Fortunately, the reader who hasn't mastered factor analysis can still understand and benefit from the book. Here is a quick attempt to explain what is, and what the debate about rotating factors is. The reader is probably familiar with tests such as the SAT which give verbal and mathematical scores, and sometimes other scores. The results of these are usually expressed by statements such as Jim earned 600 on the verbal part and 700 on the mathematical part. The reader would probably appreciate how one could also say That Jim had a total score of 1300, but did 50 points better than the typical person with a 1300 score on the mathematical part. One can express the information either way. One could base admission decisions to an engineering program on achieving a certain total score with bonus points for doing especially well on mathematics, or one could base it on a weighted average of the two scores. With suitable weights, the two computational methods would select exactly the same set of applicants. Factor analysis is merely a sophisticated way for combining scores from different tests in different ways. One of the most important facts about mental tests is that they are positively correlated. This makes it mathematically possible to condense the information on a scale into one measure, which is traditionally (among the specialists) referred to as g, for general intelligence. The mathematicians have a way of optimally combining the tests so as to give a single measure which captures as much of the information as possible in a battery of tests in this single number. That such a number can be calculated is a mere matter of mathematics. One of the main messages of this book is that most of the information in mental tests, and most of their practical utility, arises because the scores on such tests are correlated with the factor. Ones level of (i.e. intelligence) tells a lot about ability to learn, and to function in a modern economy. The reader may remember that I reviewed in this journal earlier (Miller 1996) a book titled, The Factor. This was by intelligence researcher Christopher Brand, then a lecturer at Edinburgh University. This was briefly in the bookstores. But the publisher Wiley withdrew it, because it talked about racial differences. Subsequently, Edinburgh University fired Prof. Brand. Intelligence and racial differences in it are a controversial subject and powerful interests are fighting hard to keep the public from knowing what modern science has found out about the subject (Pearson 1997). Interesting, at the same time as the UK branch of Wiley was bringing out Brand's The Factor, the US branch had Professor Jensen under contract for his book with the same title. Not surprisingly, after their action with regard to Brand's book, Wiley chose not to publish this book (in spite of its potential for selling well), and Professor Jensen had to choose another publisher, Praeger. For the readers of this journal, one of the first questions is how well predicts economic variables. …