I recently read a different handwringing article about "American high school students reading on a 5th grade level." That one was based on Accelerated Reading metrics, which rely almost entirely on syllabification. Here are some ratings I pulled up:
William Faulkner, As I Lay Dying: 5.4
Ernest Hemingway, The Sun Also Rises: 4.4
Ernest Hemingway, For Whom the Bell Tolls: 5.8
John Steinbeck, The Grapes of Wrath: 4.9
John Steinbeck, East of Eden: 5.3
Toni Morrison, Song of Solomon: 5.0
Kind of hard to believe that the Nobel Prize kept being awarded to fourth and fifth grade books, isn't it? Why don't they just award one to Beverly Cleary and be done with it? ...OR, maybe there's more to reading than the difficulty of the individual words? Just perhaps?
Smith's results surprised him. Despite deliberately choosing a mix of commercial and literary writers, he found that many of the results fell into the same range. The average in four separate categories was as follows:
The amount of passive voice the writers used ranged from 2.3% to 13.43%.
The number of characters per word ranged from 3.72 to 4.58.
The readability ranged from 72.34% to 91.84%, with an average of 83.1%.
Finally, on the Flesch-Kincaid Grade Level scale, the range was 2.68 to 6.3, with an average grade level of 4.4.
In other words, he found that the bestselling writers were aiming their prose, prose that is read by a majority of adult readers in the country, at a fourth grade level.