Table 1.

Information regarding the readability formulas used to analyse consent forms

	Flesch-Kincaid formula	SMOGa formula
Original development and reference	The formula has been designed for evaluating readability of technical texts for US military by Kincaid (Kincaid et al. 1975).	McLaughlin (McLaughlin 1969)
Analysis based on	Sentence length and syllable count	Number of complex words (3 and more syllables)
Easier formula for manual calculation (not used in this study)	G = (12*(B/W)) + (0 .4*(W/S)) – 16 G—grade level W—number of words B—number of syllables S—number of sentences	G = FLOOR(√C) + 3 G—grade level C—number of complex words (3 and more syllables) FLOOR—round the result of (√C) down to the closest perfect square.
Higher precision formula used by the software in this study	G = (11.8*(B/W)) + (0.39*(W/S)) − 15.59	G = 1.0430*√C + 3.1291

^aOriginally, McLaughlin recommended using 10 consecutive sentences from the beginning of the text, 10 sentences from the middle and 10 from the end; the formula was meant to facilitate manual calculations. In our study, the calculations were based on the whole text (and not subsamples of the text) and standardized