"Unless an individual has made the transition from word reading to reading comprehension of sentences and paragraphs, reading is neither pleasurable nor practically useful. Few adults with an IQ of eighty (the tenth percentile of the overall population norm) ever make the transition from word reading skill to reading comprehension. The problem of adult illiteracy (defined as less than a fourth-grade level of reading comprehension) in a society that provides an elementary school education to virtually its entire population is therefore largely a problem of the lower segment of the population distribution of g. In the vast majority of people with low reading comprehension, the problem is not word reading per se, but lack of comprehension. These individuals score about the same on tests of reading comprehension even if the test paragraphs are read aloud by the examiner. In other words, individual differences in oral comprehension and in reading comprehension are highly correlated."
Arthur Jensen - 1998
The g Factor;