Which index is used to calculate the reading level by counting polysyllabic words in text?

The SMOG index is a well-established tool used to assess the readability of a text by focusing specifically on polysyllabic words. This index calculates the number of words with three or more syllables in a set number of sentences. The premise behind using polysyllabic words is that they are more challenging for readers and correlate with the reading level necessary to understand the text. The formula generates a score that approximates the grade level required for comprehension, making it practical for educators and health professionals who aim to tailor written materials to their audience's reading abilities.

While other indices such as the Smith Reading index and Text Index exist, they do not specifically focus on polysyllabic words as the defining metric for estimating reading levels, which is the key characteristic that makes the SMOG index particularly relevant for this purpose.