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Table 2 Summary of readability formulae

From: Readability of patient education materials related to radiation safety: What are the implications for patient-centred radiology care?

Readability test Score Type Description Formula
Flesch–Kincaid reading grade level Grade level Part of the Kincaid Navy Personnel collection of tests. Designed for technical documents and suited to a broad array of disciplines G = (11.8 × (B/W)) + (0.39 × (W/S))  − 15.59
Flesch–Kincaid reading ease Index score (0–100) Developed to assess the readability of newspapers. Best suited to assessing school textbooks and technical manuals. Standard test used by many US government agencies. Scores range from 0–100, with higher scores denoting easier readability I = (206.835 − (84.6 × (B/W)) − (1.015 × (W/S)))
The Raygor estimate Grade Level Designed for most text, including literature and technical documents Calculated using the mean number of sentences and long words (≥ 6 characters) per 100 words, which are plotted on to a RE Graph, where their intersection determines RGL
Fry Grade level Designed for a variety of texts including technical documents and literature, across a range of levels, from primary school level to university level Calculated using the mean number of sentences and syllables per 100 words, which are plotted on to a Fry Graph, where their intersection determines RGL
SMOG Grade level Generally appropriate for secondary age (4th grade to college level) readers. Tests for 100% comprehension, whereas most formulas test for around 50–75% comprehension. Most accurate when applied to documents ≥ 30 sentences in length G = 1.0430 × √C + 3.1291
Coleman–Liau Grade level Designed for secondary age (4th grade to college level) readers. Formula is based on text from the .4 to 16.3 grade level range. Applicable to numerous sectors G = (− 27.4004 × (E/100)) + 23.06395
FORCAST Grade level Devised for assessing U.S. Army technical manuals and forms. It is the only test not designed for running narrative G = 20 − (M/10)
Gunning fog Grade level Developed to assist American businesses improve the readability of their writing. Applicable to numerous disciplines G = 0.4 × (W/S + ((C*/W) × 100))
  1. G, grade level; B, number of syllables; W, number of words; S, number of sentences; RGL, Reading Grade Level; I, Flesch Index Score; RE, Raygor Estimate; SMOG, Simple Measure of Gobbledygook; C, complex words (≥3 syllables); E , predicted Cloze percentage = 141.8401 − (0.214590 × number of characters) + (1.079812*S); M, number of monosyllabic words; C*, complex words with exceptions including, proper nouns, words made 3 syllables by addition of "ed" or "es", compound words made of simpler words