Which of the following indexes is commonly used to measure the readability of a passage?

The Flesch Reading Ease/Flesch Grade Level Index and the Gunning Fog Index are both established tools for assessing the readability of written texts. The Flesch Reading Ease formula calculates a score based on the average number of syllables per word and the average number of words per sentence, yielding a score that can indicate how easy or difficult a text is to read. A higher score suggests easier readability, while a lower score indicates that the text may be more challenging for readers.

Similarly, the Gunning Fog Index evaluates the complexity of a text by taking into account the number of words, sentences, and complex words (words with three or more syllables). It provides an estimate of the number of years of formal education required to understand the text on a first reading.

Both of these indices serve the important purpose of helping educators, writers, and readers gauge the appropriateness of reading material according to its intended audience. With the inclusion of both indices, the answer reflects the practice of utilizing multiple readability tools to provide a more comprehensive assessment of text clarity and accessibility.