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AUTOMATED READABILITY INDEX
E. A. SMITH, EdO
AEROSPACE MEDICAL RESEARCH LABORATORtIES
'R. 1. SENTER, PhD
UNIVERSITY OF CINCINNATI
I APR 41968NOVEMBER 1967
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A~1 667 273AUTOMATED READABILITY INDEX
R. J. Senter, et al
University of CincinnatiCincinnati, Ohio
DEFENSE DOCUMENTATION CENTERDEFENSE SUPPLY AGENCY
FOR FEDERAL SCIENTIFIC AND TECHNICAL INFORMATION
U. S. DEPARTMENT OF COMMERCE / NATIONAL BUREAU OF STANDARDS INSTITUTE FOR APPLIED TECHNOLOGY
AUTOMATED READABILITY INDEX
E. A. SMITH, EdD
AEROSPACE MEDICAL RESEARCH LABORATORIES
R. J. SENTER, PhD
UNIVERSITY OF CINCINNATI
.istriuLion of tlud' document is unlimited. Itmay be released/to the Clearinghouse, Depart-ment of Commerce, for sale to the general public.
This study represents a portion of the explcratory development program ofthe Technical Training Bianch of the Training Research Division. The zesearchwas conducted in part by the University of Cincinnati, under Contract AF 33(615)-1046. The work was in support of Project 1710, "Human Factors in the Design ofTraining Systems," Task 171007, "Automated Training and Programmed Instruc-tion." Dr. Gordon A. Eckstrand was the Project Scientist and Dr. Ross L. Morganwas the Task Scientist. The report covers research performed between August1964 and August 1966.
The authors are indebted to Mr. Robert J. Roettele of the Research Instru-mentation Branch for the design and construction of the Tabulator.
This technical report has been reviewed and is approved.
WALTER F. GRETHER, PhDTechnical DirectorBehavioral Sciences LaboratoryAerospace Medical Research Laboratories
Inasmuch as the utility of technical manuals is influenced to a marked extentby their reading difficulty or readability, the Automated Readability Index wasdevised to provide an easy, automated method of collecting data from whichtextual material can be evaluatczl in terms of readability. Whereas most read-ability formulae include separate jactors related to (1) word difficulty and (2)sentence difficulty, the Automate. Readability Index provides for the mechanicaltabulation of the required data on passages as they are typed on a standardtypewriter. Impulses from the typewriter activate counters which record thenumber of letters, words and sentences contained in the passage. From this, theaverage word length and average sentence length are computed. Appropriateweightings of -these factors result in an index reflecting the readability of the
passage. This index is in close agreement with other indices of readability.
IntroductionThe Air Force makes extensive use of written materials such as manuals, reports, staff studies,
training documents, letters, etc. The readability of a document greatly influences the time requiredto extract needed information from the document. Likewise, it influences the probability that theinformation extracted will be correctly understood and used. The costly effects of inadequate con-munication are well-known. Deficiencies in written communications often could be precluded bythe preparation of more readable Air Force documents. An Automated Readability Index, as de-scribed in this report, offers a fast and economical means of obtaining an index of readability ofAir Force materials such as textbooks and technical manuals. Use of such an Automated Readabil-ity Index would contribute significantly to the efficiency of many Air Force operations.
Since Chall (1958) provides an excellent source, no general review of the literature will beincluded here. Most readability indices, however, consist of two factors. One factor relates tosentence structure and is most generally a measure of the average number of words per sentence.The other factor generally relates to word structure and is usually based or, either the proportionof easy words determined with reference to word list (Dale and Chall, 1948) or the average num-r ber of syllables per word (Fleseh, 1951). While the word list has many advantages, especially in
4the lower grades, it is both slow and relatively inaccurate when applied to adult reading material.As will be demonstrated, syllable counts prove to be deceptively unreliable.To explore the reliability of a syllable count, a passage selected at random from a textbook
was presented to a class of 65 college students. This passage contained 169 syllables. The mem-bers of the class were instructed to count the number of syllables in the passage. The group'smean syllable count was 160.56. The standard deviation of the class' syllable count was 17.52,slightly more than 10 percent of tie mean. This indicates a considerable amount of variationamong syllable counters, and, consequently, of any readability based on such a count. Two weeksafter the initial administration of the syllable counting task, the same task was again presented tothe class. A "test-retest" reliability coefficient was .38 (N=64). It would appear that both inter-and intra-judge reliability for the task of syllable counting are untenable. The development ofthe Automated Readability Index is an attempt to avoid this unreliability without sacrificingvalidity.
The Automated Readability Index is derived from ratios representing word difficulty (num-ber of letters per word) and sentence difficulty (number of words per sentence). The data fromwhich the index is calculated are collected through the use of an attachment to an electric type-writer. The attachment is refered to as a Readability Index Tabulator. The Tabulator is simplycomposed of three counters (Sodeco TCe F4E .25, TCe FSE .50, and TCe F6E .50) activatedby the keyboard of the electric typewriter (IBM Selectric, model 721). These counters tabulate(a) the number of strokes, (b) the number of words, and (c) the number of sentences containedin any passage being typed. Details of the Tabulator are shown in figures 1 thn 4.
Any typist may operate this data tabulation system -. the primary modifications of standardtyping procedure necssitated by the system arc (1) an equal sign must be used in addition tothe period at the end of each sentence, and (2) the typist must space after the terminal word in
each line. During the development of the formula, these modifications were observed to bet learned rather quickly and appeared to offer only minor and temporary interference with a typist's
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FIgure 1. Typ.wrherwi0~ Tabulator
FIgure 2. PIckoff for Word Count
7 -- -
YrI1 5I S
I Figure 3. PIckoff for Sentence Count3I _
Figur* 4. Pickoff for Strokes Count (two views)
Logically, the first consideration in -the developmentof the Automated Readability Index wasto establish that the -factors used relate to those found inoother indices. The factor relating tosentence structure (average number of words per sentence) is -identical to that found in mostcurrently used -indices so no verification oit was required. The verification of the relationshipbetween the word structure factor was also virtually selfLevident. However, since -the obvious-is at times not accurate, formal verification was accomplished with regards to the- relationshipbetween the ratio used here (letters per word) and that employed by Flesch (syllables per word).A sample of 20 one-syllable words was selected at-random from Webster's New International Die-tionary. Similar samples of t