. 2017 Jun 1;2017:9780317. doi: 10.1155/2017/9780317

Table 2.

Readability test formulas used to analyze patient education websites.

Readability test	Formula
Flesch-Kincaid Grade Level	$F K G L = 0.39 (\frac{t o t a l w o r d s}{t o t a l s e n t e n c e s}) + 11.8 (\frac{t o t a l s y l l a b l e s}{t o t a l w o r d s}) - 15.59$
Flesch Reading Ease	$F R E = 206.835 - 1.015 (\frac{t o t a l w o r d s}{t o t a l s e n t e n c e s}) - 84.6 (\frac{t o t a l s y l l a b l e s}{t o t a l w o r d s})$
Gunning-Fog Score	$G F I = 0.4 [(\frac{t o t a l w o r d s}{t o t a l s e n t e n c e s}) + 100 (\frac{c o m p l e x w o r d s}{t o t a l w o r d s})]$
Coleman-Liau Index	CLI = 0.588L − 0.296S − 15.8
SMOG Index	$S M O G = 1.043 \sqrt{n u m b e r o f c o m p l e x w o r d s \times \frac{30}{t o t a l s e n t e n c e s} + 3.1291}$

Variables. Average number of letters per 100 words (L), average number of sentences per 100 words (S).

FKGL, Flesch-Kincaid Grade Level; FRE, Flesch Reading Ease; GFS, Gunning-Fog Score; CLI, Coleman-Liau Index; SMOG, Simple Measure of Gobbledygook.