Table 2. Readability indices and features.

Readability Index	Description	Formula
Flesch Reading Ease Score(FRES)	It was developed to evaluate the readability of newspapers. It is best suited for evaluating school textbooks and technical manuals. The standardized test used by many US government agencies. Scores range from 0 to 100, with higher scores indicating easier readability	I = (206.835 − (84.6 × (B/W)) − (1.015 × (W/S)))
Flesch–Kincaid grade level (FKGL)	Part of the Kincaid Navy Personnel test collection. Designed for technical documentation and suitable for a wide range of disciplines	G = (11.8 × (B/W)) + (0.39 × (W/S)) − 15.59
Simple Measure of Gobbledygook (SMOG)	It is generally suitable for middle-aged (4th grade to college level) readers. While testing 100% comprehension, most formulas test about 50%–75% comprehension. Most accurate when applied to documents ≥30 sentences long.	$G=1.0430\times \sqrt{C}+3.1291$
Gunning FOG (GFOG)	It was developed to help American businesses improve the readability of their writing. Applicable to many disciplines	G = 0.4 × (W/S + ((C∗/W)X100))
Coleman–Liau (CL) score	It is designed for middle-aged (4th grade to college level) readers. The formula is based on text in the grade level range of 0.4 to 16.3. It applies to many industries.	G = (−27.4004 × (E/100)) + 23.06395
Automated readability index (ARI)	ARI has been used by the military in writing technical manuals, and its calculation returns a grade level necessary for understanding.	ARI = 4.71 × l + 0.5∗ASL − 21.43
Linsear Write (LW)	It is developed for the United States Air Force to help them calculate the readability of their technical manuals	LW = (R + 3C)/S Result • If >20, divide by 2 • If ≤20, subtract 2, and then divide by 2

Notes.

G

Grade level

B

Number of syllables

W

Number of words

S

Number of sentences

I

Flesch Index Score

SMOG

Simple Measure of Gobbledygook

C

Complex words (≥3 syllables)

E

predicted Cloze percentage=141.8401 - (0.214590 ×number of characters) + (1.079812 ∗S)

C ∗

Complex words with exceptions including, proper nouns, words made three syllables by addition of “ed” or “es”, compound words made of simpler words

ASL

the average number of sentences per 100 words

R

the number of words ≤2 syllables