Readability

Readability is the ease with which a reader can understand a written text. The concept exists in both natural language and programming languages though in different forms. In natural language, the readability of text depends on its content and its presentation. In programming, things such as programmer comments, choice of loop structure, and choice of names can determine the ease with which humans can read computer program code.
Higher readability in a text eases reading effort and speed for the general population of readers. For those who do not have high reading comprehension, readability is necessary for understanding and applying a given text. Techniques to simplify readability are essential to communicate a set of information to the intended audience.

Definition

The term "readability" is inherently broad and can become confusing when examining all of the possible definitions. Readability is a concept that involves audience, content, quality, legibility, and can even involve the formatting and design structure of any given text. Different definitions of readability exist from various sources. The definition fluctuates based on the type of audience to whom one is presenting a certain type of content. For example, a technical writer might focus on clear and concise language and formatting that allows easy-reading. In contrast, a scholarly journal would use sophisticated writing that would appeal and make sense to the type of audience to whom they are directing information.

Applications

Readability is essential to the clarity and accessibility of texts used in classrooms, work environments, and everyday life.
Much research has focused on matching prose to reading skill, resulting in formulas for use in research, government, teaching, publishing, the military, medicine, and business. Readability measurement in non-English languages has also been the focus of various studies.
The two publications with the largest circulations, TV Guide and Reader's Digest, are written at the 9th-grade level. The most popular novels are written at the 7th-grade level. This supports the fact that the average adult reads at the 9th-grade level. It also shows that, for recreation, people read texts that are two grades below their actual reading level.

History

Early research

For centuries, teachers and educators have seen the importance of organization, coherence, and emphasis in good writing. In the 1880s, English professor L. A. Sherman found that the English sentence was getting shorter. In Elizabethan times, the average sentence was 50 words long while in Sherman's modern time, it was 23 words long.
In 1889 in Russia, the writer Nikolai A. Rubakin published a study of over 10,000 texts written by everyday people. From these texts, he took 1,500 words he thought most people understood. He found that the main blocks to comprehension are unfamiliar words and long sentences. Starting with his own journal at the age of 13, Rubakin published many articles and books on science and many subjects for the great numbers of new readers throughout Russia. In Rubakin's view, the people were not fools. They were simply poor and in need of cheap books, written at a level they could grasp.

Reading ease

The earliest reading ease assessment is the subjective judgment termed text leveling. Formulas do not fully address the various content, purpose, design, visual input, and organization of a text. Text leveling is commonly used to rank the reading ease of texts in areas where reading difficulties are easy to identify, such as books for young children. At higher levels, ranking reading ease becomes more difficult, as individual difficulties become harder to identify. This has led to better ways to assess reading ease.
In the 1920s, the scientific movement in education looked for tests to measure students' achievement to aid in curriculum development. Teachers and educators had long known that, to improve reading skill, readers—especially beginning readers—need reading material that closely matches their ability. University-based psychologists did much of the early research, which was later taken up by textbook publishers. In 1921, Harry D. Kitson published The Mind of the Buyer, one of the first books to apply psychology to marketing. Kitson's work showed that each type of reader bought and read their own type of text. On reading two newspapers and two magazines, he found that short sentence length and short word length were the best contributors to reading ease.
In 1923, Bertha A. Lively and Sidney L. Pressey published the first reading ease formula. They were concerned that junior high school science textbooks had so many technical words and that teachers would spend all class time explaining these words. They argued that their formula would help to measure and reduce the "vocabulary burden" of textbooks. Their formula used five variable inputs and six constants. For each thousand words, it counted the number of unique words, the number of words not on the Thorndike list, and the median index number of the words found on the list. Manually, it took three hours to apply the formula to a book.
After the Lively–Pressey study, people looked for formulas that were more accurate and easier to apply. In 1928, Carleton Washburne and Mabel Vogel created the first modern readability formula. They validated it by using an outside criterion, and correlated.845 with test scores of students who read and liked the criterion books. It was also the first to introduce the variable of interest to the concept of readability.
Between 1929 and 1939, Alfred Lewerenz of the Los Angeles School District published several new formulas.
In 1934, educational psychologist Edward Thorndike of Columbia University noted that, in Russia and Germany, teachers used word frequency counts to match books to students. Word skill was the best sign of intellectual development, and the strongest predictor of reading ease. In 1921, Thorndike published Teachers Word Book, which contained the frequencies of 10,000 words. He also published his readability formula. He wrote that word skills can be increased if the teacher introduces new words and repeats them often. In 1939, W.W. Patty and W. I Painter published a formula for measuring the vocabulary burden of textbooks. This was the last of the early formulas that used the Thorndike vocabulary-frequency list. Until computers came along, word frequency lists were the best aids for grading reading ease of texts.
In 1981 the World Book Encyclopedia listed the grade levels of 44,000 words. A popular strategy amongst educators in modern times is "incidental vocabulary learning," which enforces efficiency in learning vocabulary in the short-term rather than drilling words and meanings teachers hope will stick. The incidental learning tactic is meant to help learners build comprehension and learning skills rather than memorizing words. Through this strategy, students would hopefully be able to navigate various levels of readability using context clues and comprehension.

Readability studies

During the Great Depression of the 1930s, the U.S. government invested in adult education. In 1931, Douglas Waples and Ralph Tyler published What Adults Want to Read About. It was a two-year study of adult reading interests. Their book showed not only what people read but what they would like to read. They found that many readers lacked suitable reading materials: they would have liked to learn but the reading materials were too hard for them.
Lyman Bryson of Teachers College, Columbia University found that many adults had poor reading ability due to poor education. Even though colleges had long tried to teach how to write in a clear and readable style, Bryson found that it was rare. He wrote that such language is the result of a "...discipline and artistry that few people who have ideas will take the trouble to achieve... If simple language were easy, many of our problems would have been solved long ago." Bryson helped set up the Readability Laboratory at the college. Two of his students were Irving Lorge and Rudolf Flesch.
In 1934, Ralph Ojemann investigated adult reading skills, factors that most directly affect reading ease, and causes of each level of difficulty. He did not invent a formula, but a method for assessing the difficulty of materials for parent education. He was the first to assess the validity of this method by using 16 magazine passages tested on actual readers. He evaluated 14 measurable and three reported factors that affect reading ease.
Ojemann emphasized the reported features, such as whether the text was coherent or unduly abstract. He used his 16 passages to compare and judge the reading ease of other texts, a method now called scaling. He showed that even though these factors cannot be measured, they cannot be ignored.
Also in 1934, Ralph Tyler and Edgar Dale published the first adult reading ease formula based on passages on health topics from a variety of textbooks and magazines. Of 29 factors that are significant for young readers, they found ten that are significant for adults. They used three of these in their formula.
In 1935, William S. Gray of the University of Chicago and Bernice Leary of Xavier College in Chicago published What Makes a Book Readable, one of the most important books in readability research. Like Dale and Tyler, they focused on what makes books readable for adults of limited reading ability. Their book included the first scientific study of the reading skills of American adults. The sample included 1,690 adults from a variety of settings and regions. The test used a number of passages from newspapers, magazines, and books—as well as a standard reading test. They found a mean grade score of 7.81. About one-third read at the 2nd to 6th-grade level, one-third at the 7th to 12th-grade level, and one-third at the 13th–17th grade level. The authors emphasized that one-half of the adult population at that time lacked suitable reading materials. They wrote, "For them, the enriching values of reading are denied unless materials reflecting adult interests are adapted to their needs." The poorest readers, one-sixth of the adult population, need "simpler materials for use in promoting functioning literacy and in establishing fundamental reading habits."
In 1939, Irving Lorge published an article that reported other combinations of variables that indicate difficulty more accurately than the ones Gray and Leary used. His research also showed that, "The vocabulary load is the most important concomitant of difficulty." In 1944, Lorge published his Lorge Index, a readability formula that used three variables and set the stage for simpler and more reliable formulas that followed.
By 1940, investigators had:

Successfully used statistical methods to analyze reading ease
Found that unusual words and sentence length were among the first causes of reading difficulty
Used vocabulary and sentence length in formulas to predict reading ease