Hull devised four cloze tests of each of five criterion passages from the Kincaid study. The first test was the original passage. Each of the other tests increased one of three indicators of modifier load by at least 50%: density of modifiers, ambiguity of modifiers, and density of prepositions. The subjects were 107 science, engineering, and management students enrolled in a senior course in technical and professional communication at Rensselaer Polytechnic Institute.

The mean cloze scores on the five unaltered passages correlated (r = ) 0.882 with the Kincaid reading-grade levels assigned to these passages. This result justified both the subject sampling and the use of the test results to produce a new formula. The test results confirm the negative effect (r = -0.664) of modifier density on comprehension. They also indicated that sentence length is a valid indicator for technical material, perhaps better than word difficulty (contrary to previous research).

Hull developed first formula with five variables, which accounts for (r2 = ) 68% of passage difficulty. Like others before him, he found that the difficulty of using a larger number of variables reduces the reliability of the formula and makes it impractical. He created a another formula, shown here, that uses only sentence length and the density of modifiers (called prenomial modifiers) and accounts for (r2 = ) 48% of passage difficulty. Though slightly less valid than the Kincaid formula, it is as accurate as many other popular formulas:

Grade level = 0.49 (average sentence length) + 0.29 (prenomial modifiers per 100 words) - 2.71

In the conclusion of his paper, Hull advises technical writers that using shorter sentences reduces their complexity and makes them easier to read. He also recommends eliminating strings of nouns, adjectives, and adverbs as modifiers. Instead, writers should use prepositional phrases and place adjectives in the predicate position (after the verb) rather than in the distributive position (before the noun).

Degrees of Reading Power (DRP) In 1981, the College Entrance Examination Board dropped its use of grade-level reading scores and adopted the Degrees of Reading Power (DRP) system developed by Touchstone Applied Science Associates (Koslin et al. 1987, Zeno et al. 1995).

The DRP uses the Bormuth Mean Cloze formula to predict scores on a 0 (easy) to 100 (difficult) scale, which can be used for scoring both text readability and student reading skills. The popular children's book Charlotte's Web has a DRP value of 50. Likewise, students with DRP test scores of 50 (at the independent level) are capable of reading Charlotte's Web and easier texts independently. The Board also uses this system to provide readability reports on instructional materials used by school systems.

Computerized writing aids Beginning in the 1980s, the first computer programs appeared that not only contained the formulas but also other writing aids. The Writer's Workbench, developed at Bell Laboratories became the most popular of these (Macdonald, Frase, Gingrich, and Keenan 1982). It contains several readability indexes, stylistic analysis, average lengths of words and sentences, spelling, punctuation, faulty phrases, percentages of passive verbs, a reference on English usage, and many other features.

Kincaid, Aagard, O'Hara, and Cottrell (1981) developed CRES, a computer readability editing system for the U.S. Navy. It contains a readability formula and flags uncommon words, long sentences, and offers the writer alternatives.

Today, popular word processors such as Microsoft Word and Corel WordPerfect include a combination of spell checkers, grammar checkers, and readability formulas to help in creating texts that are more readable. Note that the Flesch-Kincaid Grade Level in Word's Readability Statistics is defective in that it only goes to the 12th grade.