From the 29 factors that had been found significant for children's comprehension, they found ten that were significant for adults. They found that three of these factors correlated so highly with the other factors that they alone gave almost the same prediction as the combined ten. They were:

• Number of different technical words.
• Number of different hard non-technical words.
• Number of indeterminate clauses.

They combined these three factors into a formula to predict the proportion of adult readers of limited reading ability who would be able to understand the material. The formula correlated .511 with difficulty as measured by multiple-choice reading tests based on the 74 criterion selections.

The Ojemann and Dale-Tyler studies mark the beginning of work on adult formulas that would continue unabated until the present time.

Lyman Bryson: Books for the average reader During the depression of the 1930's, the government in the U.S. put enormous resources into adult education. Bryson Lyman first became interested in non-fiction materials written for the average adult reader while serving as a leader in adult-education meetings in New York City. What he found was that what kept people from reading more was not lack of intelligence, but the lack of reading skills, a direct result of limited schooling.

He also found out there is a tendency to judge adults by the education their children receive and to assume the great bulk of people have been through high school. At that time, 40 to 50 million people had a 7^th to 9^th grade education and reading ability.

Writers had assumed that readers had an equal education to their own or at least an equal reading ability. Highly educated people failed to realize just how much easier it is for them to read than it is for an average person. They found it difficult to recognize difficult writing because they read so well themselves.

Although college and business courses had long promoted ideas expressed in a direct and lucid style, Bryson found that simple and clear language was rare. He said such language results from "a discipline and artistry which few people who have ideas will take the trouble to achieve... If simple writing were easy, many of our problems would have been solved long ago" (Klare and Buck, p. 58).

Bryson helped set up the Readability Laboratory of the Columbia University Teachers College with Charles Beard and M. A. Cartwright. The purpose of the laboratory was not to rewrite the classics or to help the beginning reader. The purpose was to produce readable books on serious subjects for the average citizen.

Bryson understood that people with enough motivation and time could read difficult material and improve their reading ability. Experience, however, showed him that most people do not do that.

Perhaps Bryson's greatest contribution was the influence he had on his two students, Irving Lorge and Rudolf Flesch.

Gray and Leary: what makes a book readable William S. Gray and Bernice Leary (1935) published a landmark work in reading research, What Makes a Book Readable. Like Dale and Tyler's work, it attempted to discover what makes a book readable for adults of limited reading ability.

Their criterion included 48 selections of about 100 words each, half of them fiction, taken from the books, magazines, and newspapers most widely read by adults. They established the difficulty of these selections by a reading-comprehension test given to about 800 adults designed to test their ability to get the main idea of the passage.