Readability and Intelligibility Formulas

Readability and intelligibility formulas evaluate the reading skill level required to understand a document. Results are generally expressed in terms of grade level.

Readability formulas can provide an initial overview of a text’s level of difficulty in terms of wording (vocabulary and syntax). The best-known formulas^{Footnote 1} are:

• Flesch formulas or Reading Ease Level tests – evaluate the number of syllables per word and number of words per sentence;
• Gunning formula or Fog index – evaluates the average length of sentences and the number of multi-syllable words;
• Dale-Chall formulas – compare the words in the documents with a list of known words for a given grade level.

Intelligibility formulas, which are more complex, deal with the organization and presentation of information. They evaluate the complexity of the tasks required to understand text structure, identify the subject and follow the flow of ideas and, in general, measure information density.^{Footnote 2}

However, these formulas do not evaluate the capacity for in-depth comprehension of a text based on the communication situation and, therefore, cannot guarantee the effectiveness of communication. They are subject to the following limits:

• they do not take into account the readers’ true abilities and their motivation;
• they are hard to apply when evaluating forms, tables, illustrations or other visual aspects;
• they do not show the writer the type of changes to be made, except for complex words and sentences that are too long.

Public Opinion Research

Public opinion research offers the possibility of evaluating communication initiatives, by practical testing or surveys, from the perspective of people with low literacy skills. Such research also makes it possible to measure the impact and the desired outcome (relevance, comprehension and persuasion).

Tab 7, Contacts, provides a list of literacy organizations. These organizations can play an important role in recruiting persons with low literacy skills for public opinion research.

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