Readability evaluation tools

Four readability scales, each of which uses different techniques, were used to evaluate the readability of the websites: Flesch-Kincaid Grade Level (FKGL), Simple Measure of Gobbledygook (SMOG), Gunning Fog, and Flesch Reading Ease Score (FRE). These scales have been used in many readability evaluation studies of health websites on various topics and are reliable [46–53], and NIH recommends using FKGL, Gunning Fog, and SMOG for readability evaluations [54].

The FRE scale produces a score between 0 and 100, with higher scores indicating higher readability levels: scores of 90–100, 60–70, and 0–30 indicate that text can be understood by fifth-grade students, eighth- or ninth-grade students, and university graduates, respectively. The Gunning Fog scale produces scores of 5, 10, 15, or 20, which indicate that text is easy to read, hard to read, difficult to read, or very difficult to read, respectively. The SMOG and FKGL scales estimate the years of education a person needs to have completed to understand a written text; for example, a score of 7.4 indicates that a seventh-grader can understand the text. To apply these scales, a free online readability checker (Readability Formulas) was utilized [55]. This web-based tool has been used in readability evaluations of a wide variety of health-related websites [36, 46, 50, 56–59].