Throughout the world, almost 800 million people are illiterate, mainly due to economic reasons rather than because of low intelligence. Most people with low literacy skills have average IQs and function quite well by compensating in other ways for the lack of reading skills.
In terms of the U.S. population, most are white native-born Americans, and are found in every walk of life. On a percentage basis, more minorities and immigrants do have reading difficulties.
Since there is a strong social stigma attached to illiteracy, nearly all nonreaders or poor readers will seek to conceal this fact. They will use ruses such as, “I forgot my glasses,” or, “I’ll have to take this home for my husband [wife] to see it first,” or, “My eyes are tired.” Consequences can be serious if medication directions are not followed, or merely inconvenient for client who could not read a sign.
Years of schooling tells what people have been exposed to, not what reading skill they acquired. Surveys have shown that, on average, adults currently read three to five grade levels lower than the years of schooling completed. Through disuse, the reading skills of many adults have atrophied.
The above was adapted from the following: Doak, C.C., Doak, L.G., & Root, J.H., (1996). Teaching patients with low literacy skills, (2nd Edition). Philadelphia, PA: J.B. Lippincott Company.