Abstract Background Understanding trial information is essential for participants to give truly informed consent. Current guidance suggests that health information should be accessible to readers with a reading age of 11 years. Readability describes how easily text can be understood, while reading age represents the minimum age at which a typical reader is likely to be able to understand the material. This study examines the readability and reading age of participant information leaflets (PILs) used in recent phase I clinical trials to assess how well they align with recommended standards. Methods This single-centre study analysed phase I participant information leaflets (PILs) produced between 2017 and 2022. Five established readability tools were used to assess readability and reading age: Flesch Reading Ease, Flesch-Kincaid Grade Level, Gunning Fog Index, Fry Readability and Simple Measure of Gobbledygook (SMOG) Index. Readability was compared between academic and industry-developed PILs. Results A total of 46 PILs were analysed in this study: 38 (82.6%) industry and 8 (17.4%) academic-led clinical trials. PILs had a mean (± SD) total word count of 8426 (± 2002). The overall mean readability scores, and equivalent reading ages were as follows: Flesch Reading Ease: 53.5 – age 15 + ; Flesch-Kincaid Grade Level: 9.9 – age 14–15; Gunning Fog Index: 11.6 – age 16–17; Fry Readability: 9.9 – age 14–15; SMOG: 13.5 – age 19 + . Academic PILs were more readable than industry PILs, with statistically significant differences for the Flesch Reading Ease (p = 0.046), Gunning Fog Index (p = 0.035), Fry Readability (p = 0.041), and SMOG Index (p = 0.010). No significant difference was observed for the Flesch–Kincaid Grade Level. Conclusions All PILs were written at a reading age far above recommended levels, raising concerns that many potential participants, particularly those with lower literacy or living in areas of higher deprivation, may struggle to understand essential trial information or may be deterred from taking part altogether. While readability formulas capture only one dimension of comprehensibility, these findings highlight an urgent need to redesign PILs to reduce reading age and to evaluate how improving readability impacts participant understanding and informed consent.
Dodd et al. (Thu,) studied this question.