These factors include the legibility of the print and illustrations, the motivation and interest of the reader, and the reading level of the text in relation to the reading ability of the reader (Johnson, 1998). These key ideas of readability are at the heart of choosing the best textbooks for students. There are many readability formulas or indexes teachers can use to objectively measure the readability of textbooks. Many readability formulas have been developed as a result of research evidence (Johnson, 1998).
Most readability formula and index values are calculated by measuring sentence length and word familiarity or word length to determine a grade-level score for text passages (Vacca, 2002). There are several widely used readability formulas. The Fry Readability Graph was developed by Edward Fry in 1977 for the purpose of predicting readability. It is a quick and simple readability formula. He used the common formula variables of syllables per 100 words and words per sentence.
The user marks the counts of the variables on a graph and then reads the readability grade score directly from it. The graph was designed to identify the grade-level score for materials from grade 1 though college and can predict the difficulty of the material within one grade level (Vacca, 2002). Flesch-Kincaid Formula was developed to be used as a US Government Department of Defense standard test. The formula uses two factors: the average number of syllables per 100 words and the average number of words per sentence.
The score in this case indicates a grade level (Johnson, 1998). Flesch-Kincaid Grade Level Index is automatically calculated on Microsoft® Word documents. Microsoft® Word will display readability statistics after it has completed a grammar check, which is accessible from the tool bar (Arnold, n. d. ). Dale-Chall Readability Formula has a 3,000 “familiar word” list which is used as a guide to identify “difficult words”. This formula uses two factors: the average sentence length and the percentage of unfamiliar, or difficult, words (Intervention, n. . ). Gunning’s ‘FOG’ Readability Formula is suitable for secondary and older primary age groups. Gunning proposed counting words of three or more syllables, assigning them as “hard words”. The formula is based on two counts, that of average sentence length and the percentage of “hard words” (Johnson, 1998). The ‘SMOG’ Formula tends to give higher values than the other formulas because it was intended to predict the level necessary for 90 – 100% comprehension of the reading material, i. e. when the SMOG formula yields a readability score of ten for a particular textbook, the students reading on a tenth grade level will be reading the material with 90 to 100% accuracy (Johnson, 1998). FORCAST Formula was devised for assessing US army technical manuals and is not suitable for primary age materials. But, because it is one of the only formulas that does not need whole sentences, it is suitable for assessing notes and test questions. The only factor used to calculate the FORCAST formula is the number of single-syllable words found in a sample of 150 total words (Johnson, 1998).
According to Vacca (2002), the Close Procedure does not use a formula to determine readability. This procedure determines how well students can read a particular reading passage as a result of their interaction with the reading material. In this method every nth word is deleted from the passage, leaving a blank in its space. The passage is given to students to fill in the missing words and the completed passage is used to evaluate students’ ability to accurately supply the missing words.
The General Textbook Readability Checklist is a checklist that focuses on the understandability, usability, and interestability of a textbook. This purpose of this study was to examine textbook readability by applying several readability formulas, including the Fry Readability Graph, Flesch-Kincaid Formula, Flesch-Kincaid Grade Level Index, Dale-Chall Readability Formula, Gunning ‘FOG’ Readability Formula, McLaughlin ‘SMOG’ Formula, FORCAST Formula, Cloze Procedure and the General Textbook Readability Checklist, to a biology textbook titled, Modern Biology.
Method Materials Materials used in this study included a 10th grade biology textbook, Modern Biology as well as the procedural guidelines for each of the readability formulas that will be used to assess the textbook. Procedure 18 passages were randomly selected from the Modern Biology textbook and the appropriate pages photocopied.
The photocopied passages were then placed into 5 groups having three samples each (Fry Readability Graph Group- Appendix A, Flesch-Kincaid Formula Group- Appendix B, Dale-Chall Readability Formula Group –Appendix D, Gunning ‘FOG’ Readability Formula Group- Appendix E, and FORCAST Formula Group- Appendix G), and three separate groups containing one passage each (Flesch-Kincaid Grade Level Index Group- Appendix C, McLaughlin ‘SMOG’ Formula Group- Appendix F, and Cloze Procedure Group- Appendix H). A more subjective measure was used in the General Textbook Readability Checklist (Appendix I).
Procedures were followed for each of the Formulas and Indexes, and results were tabulated and reported. A brief summary and discussion were included in the write-up. Results and Discussion This purpose of this study was to examine textbook readability by applying several readability formulas, including the Fry Readability Graph, Flesch-Kincaid Formula, Flesch-Kincaid Grade Level Index, Dale-Chall Readability Formula, Gunning ‘FOG’ Readability Formula, McLaughlin ‘SMOG’ Formula, FORCAST Formula, Cloze Procedure and the General Textbook Readability Checklist, to a biology textbook titled, Modern Biology.
As table 2 illustrates, the Flesch-Kincaid Formula (10. 8 grade, 15. 8 years old) was the only readability method that supported the teacher’s decision to use this textbook. The Fry Readability Graph (Table 1) indicated that the textbook was at an 8th grade level (13 years old). The remaining objective methods for readability, Flesch-Kincaid Grade Level Index refer to Table 3 (12 grade), Dale-Chall Readability Index (Table 4 -16 grade), Gunning ‘FOG’ Readability refer to Table 5 (13. 6 grade, 18. 6 years old), McLaughlin ‘SMOG’ Formula see Table 6 (13. 1 grade, 18. 1 years old), and the FORCAST Formula see Table 7 (12. grade, 17. 1 years old) indicated that the textbook reading would be too difficult for a 10th grader. In an attempt to produce a more cohesive point on the scale of readability, the averages of six tests (Fry Readability Graph, Flesch-Kincaid Formula, Dale-Chall Readability Index, Gunning ‘FOG’ Readabilty, McLaughlin ‘SMOG’ Formula, and the FORCAST Formula) were found for the textbook. As illustrated in Table 10, the average grade for this text is found to be at the 12th grade. The Close Readability Procedure results also indicate that the reading level is to difficult for the 10th grade class (Table 8).
According to the General Textbook Readability Checklist the textbook is strongest in its usability and weakest in its understandability (Table 9). I really am not surprised that the results indicate that the textbook is too difficult for the 10th grade student. Science textbooks are probably inherently more difficult to read because the subject matter is more complex as is the terminology. Although these tests didn’t provide the desired results, there is a lot of similarities between them and I believe that they are still good measures of the readability of textbooks.