|
In The Technique of Clear Writing, Gunning (1952) published his own
readability formula developed for adults, the Fog Index, which became popular
because of its ease of use. It uses two variables, average sentence length and the
number of words with more than two syllables for each 100 words.
Grade Level = .4 (average sentence length + hard words)
Where:
Hard words = number of words of more than two syllables
Gunning developed his formula using a 90% correct-score with the McCall-Crabbs
reading tests. This gives the formula a higher grade criterion than other
formulas except for McLaughlin's SMOG formula, which is based on a 100%
correct-answer criterion. The grade-level scores predicted by these two formulas
tend to be higher than other formulas.
Gunning found that popular magazines were consistent in their reading levels
over time. He published these correlations between reading levels of different
classes of magazines and their total circulation (p. 35). See Table 6.
| Group | Approx. Total Circulation | Average Sentence Length |
Percentage of Hard Words | Total | Fog Index |
| Class | Fewer than 1 million | 20 | 10 | 30 | 12 |
| News | About 3 million | 16 | 10 | 26 | 10 |
| Reader's Digest | 8 million | 15 | 7 | 22 | 9 |
| Slicks | More than 10 million | 15 | 5 | 20 | 8 |
| Pulps | More than 10 million | 15 | 3 | 16 | 6 |
Table 6. Gunning's analysis of the readability of adult reading materials.
The validation of the original Fog formula has never been published. According
to this author's calculations, however, it correlates .93 with the normed reading
texts of Chall et al. (1996), a figure which may account for its popularity.
Sumner, and Kearl (1958) recalculated the Fog formula using the McCall-Crabbs
reading lessons. The recalculated Fog formula, shown here, correlates .59 with
the reading passages.
Grade level = 3.0680 + .0877 (average sentence length) + .0984 (percentage
of monosyllables)
The publication of the Flesch, Dale-Chall, and Gunning formulas conveniently
marks the end of the first stretch of readability development. The authors of
these formulas brought the issue of readability to public attention. They
stimulated new consumer demands for documents in plain language. Finally,
they stimulated new studies, not only on how to improve the formulas, but also
on the other factors affecting reading success.
THE NEW READABILITY STUDIES
The new readability was a period of consolidation and deeper study.
Investigators sought to learn more about how the formulas work and how to improve them.
In the 1950s, several other developments accelerated the study of readability.
The challenges of Sputnik and the demands of new technologies created a need
for higher reading skills in all workers. While the older manufacturing industries
had little demand for advanced readers, new technologies required workers with
higher reading proficiency.
|