Background: The readability of written texts aimed at patients is an indicator of quality. Szigriszt made an adaptation of the RES Flesch Score, calling it "Escala de Nivel de Perspicuidad" (Clarity Level Scale), to measure the difficulty in reading a text. But Szigriszt used a text sample that was neither representative nor random, which is why the conclusions are not sufficiently consistent. The aim of this article is to complete the process begun by Szigriszt, review the Szigriszt Scale, comparing it with Flesch's scale, and propose a scale according to Spanish reading habits.
Methods: Descriptive study. Two hundred and ten documents of 3 types were selected at random: Stationary magazines, school textbooks and scientific magazines. Three fragments of at least 500 words were chosen at random from each one, from the beginning, middle and end. The Flesch-Szigriszt Index (Indice de Legibilidad de Flesch-Szigriszt [IFSZ]), available on the INFLESZ program, was calculated. The scores were classified according to the Flesch and Szigriszt scales.
Results: The readability of the stationary magazines is 60, of scientific magazines 37.9, and school textbooks 67.39.
Conclusions: Only the scientific magazines are situated between 0 and 50. There are no publications with scores lower than 15. Szigrsizt locates "Normal" from 50; Flesch from 60. An intermediate position is adopted and a new scale is proposed: the INFLESZ Scale, which establishes 5 sections: "Very difficult" (<80), "Somewhat difficult" (40-55), "Normal" (55-65), "Quite easy" (65-80) and "Very easy" (>80). Neither the Clarity Level Scale of Szigriszt nor the RES Flesch Score are adapted to Spanish reading habits. In the case of texts on health, there is a greater probability of their being read and understood if they exceed 55.