Teachers are frequently required to review a number of textbooks in order to select one that is suitable for their classes. Text suitability depends not only on content, but also on the reading level at which the textbook is written. The suitability of content can be determined by comparing the material in the text with the goals and objectives of the course. However, comparing the reading level of the text to the reading level of the students is often a difficult task for teachers. Student reading levels can be determined through various achievement and/or reading tests. Accurately determining the reading level of a text is much more difficult. Two factors, sentence length and number of syllables per word, are the basis of most reading-level formulas. They require complex calculations, time-consuming procedures, or both; thus, most formulas are not easy for the classroom teacher to use. It would seem reasonable to assume that the specialized vocabulary used in would have a substantial impact on the readability of a text. However, Daugs and Daugs (1974), in studying the readability of the BSCS text Molecules to Man, concluded that science vocabulary is not a major contributor to difficulty. Relatively simple methods for determining the reading level of a textbook have recently become available. One of these, the Readability Graph, was developed by Edward Fry. He plotted the number of syllables in the words used and the sentence length for a number of books that had been assigned reading levels by their publishers. The curve was then smoothed and, after some trial use, correlational studies were run. The grade-level areas were then adjusted. The resulting curve with grade-level areas indicated is shown in figure 1. The Readability Graph was used in this study of the reading level of selected high school biology texts. How well does the Readability Graph serve its intended purpose, and how accurate are the results? Fry (1968) states that the Readability Graph results are probably accurate to within a grade level. How well do the results correlate with other reading level determinations? Fry reports on the correlations with five other reading-level formulas. The correlations obtained are: Graph for Estimating Readability
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