The authors obtained the familiarity scores by giving a three-choice test to students from the 4^th to the 16^th grade in schools and colleges throughout the U.S. The editors of the encyclopedia also used the scores to test the readability of the articles they published. Field tests of the encyclopedia later confirmed the validity of the word scores. This work is exceptional in every respect and is considered by many to be the best aid in writing for a targeted grade level.

Fig. 3. Sample entries from The Living Word Vocabulary. This work featured not only grade level and a short definition, but also the percentage of readers in that grade who know the word. The editors of World Book Encyclopedia used this information as one of the reading-level tests for their entries (Dale and O'Rourke 1981).

In the preface, the Editorial Director of the encyclopedia W. H. Nault wrote (p. v) that this work marked "the beginning of a revolutionary approach to the preparation and presentation of materials that fit not only the reading abilities, but the experience and background of the reader as well."

Although this work is out of print, you can find it at libraries and used bookshops along with other graded vocabularies and word-frequency lists such as The American Heritage Word Frequency Book.

The classic readability formulas

Harry D. Kitson - Different readers, different styles Psychologist Harry D. Kitson (1921) published The Mind of the Buyer, in which he showed how and why readers of different magazines and newspapers differed from one another. Although he was not aware of Sherman's work, he found that sentence length and word length measured in syllables are important measures of readability. Rudolph Flesch would incorporate both these variables in his Reading Ease formula 30 years later.

Although Kitson did not create a readability formula, he showed how his principles worked in analyzing two newspapers, the Chicago Evening Post and the Chicago American and two magazines, the Century and the American. He analyzed 5000 consecutive words and 8000 consecutive sentences in the four publications. His study showed that the average word and sentence length were shorter in the Chicago American newspaper than in the Post, and the American magazine's style simpler than the Century's, accounting for the differences in their readership.