Persuasive Communication - How Audiences Decide. 2nd Edition

158 Understanding Rational Decision Making

the next section. As Chapter 3 explains, sentence comprehension involves three major subprocesses:

syntactic analysis, semantic analysis, and referential representation.^135 Aids to each of these three

subprocesses make sentence comprehension easier.

Short Words and Sentences

Aids to the fi rst sentence-comprehension subprocess, syntactic analysis, make it easier for the

audience to determine the grammatical role each word plays in a sentence. Because a rough

measure of syntactic complexity is sentence length, longer sentences tend to be more diffi cult

to comprehend than shorter ones.^136 Syntactic analysis becomes even more diffi cult when the

individual words in a sentence are long, complex in meaning, or infrequently used.^137 Thus, two

aids to sentence comprehension would appear to be the use of short sentences and easily under-

stood short words.

Readability formulas implicitly advocate keeping words and sentences short as an aid to reading

comprehension. The formulas use sentence length and word length to estimate the diffi culty or

ease of comprehending prose passages. Readability formulas are based on studies that show syntac-

tic complexity and vocabulary diffi culty account for a large proportion of the variance in reading

comprehension.^138 Other studies show that sentence length and word length also determine read-

ing speed.^139

Three popular readability formulas are the Flesch readability formula,^140 the FOG index read-

ability formula,^141 and the Dale-Chall readability formula (see Table 4.1).^142 All three formulas

use word and sentence length as proxies for word familiarity and sentence complexity. The Flesch

formula assigns passages of prose a reading ease score, 100 being the easiest and 0 being the most

diffi cult. The FOG index and the Dale-Chall formula both assign passages a reading grade level

from 1 to 12, 1 indicating that the passage could be understood by the typical fi rst grader.

Other readability formulas such as the Flesch-Kincaid readability formula,^143 the New

Dale-Chall readability formula,^144 Lexile,^145 and Degrees of Reading Power (DRP)^146 also use word

and sentence length as proxies for word familiarity and sentence complexity.^147 Although not a

perfect measure of reading diffi culty, the New Dale-Chall formula may be the most valid of the

popular traditional readability formulas.^148 The formulas that Lexile and DRP use to compute

reading diffi culty are not publically released, but their scores for texts are highly correlated with

Flesch-Kincaid readability scores.^149

Despite the fact that ideas expressed in short words and sentences are usually easier to com-

prehend than ideas expressed in longer words and sentences, it is debatable whether readability

formulas are useful guidelines for revising diffi cult-to-comprehend sentences and discourse.^150 On

the one hand, shortening long sentences has been shown to aid readers’ understanding of written

prose.^151 On the other hand, a number of studies show that improving readability as measured by

readability formulas does not reliably affect readers’ comprehension or recall of material.^152

TABLE 4.1 How Three Readability Formulas Calculate Reading Ease

The Flesch readability formula calculates reading ease as follows: Reading ease =
206.835 − .846(number of syllables per 100 words) − 1.015(average number of words per sentence)

The FOG index is very similar: Reading grade =
.4(average number of words per sentence + percentage of words of more than two syllables)

In the Dale-Chall formula, word familiarity replaces syllable length: Reading grade =
.16(percentage of uncommon words) + .05(average number of words per sentence)