A Pilot Study to Explore Length and Readability Characteristics of Subject Information Sheets/Informed Consent Forms of Clinical Trial Applications in the EU

The Clinical Trials Information System (CTIS) enables a central joint registration of clinical trials in the EU and provides public access to key trial documents including informed consent documents. The increasing complexity and length of subject information sheets and informed consent forms (SIS/ICFs) can impact participant comprehension and willingness to enroll in a trial. This pilot study aimed to analyze the characteristics of actual SIS/ICFs from a sample of approved CTIS submissions, with a focus on Phase III trials. We consulted the CTIS public database to retrieve authorized Phase III trials. The final dataset comprised 67 drug trials submitted between January 1, 2023, and November 16, 2023. SIS/ICF page and word count, and readability scores were compared across countries, sponsorship, and other trial-related characteristics. Exploratory analyses assessed document structure and page space utilization. The median SIS/ICF length was 16 pages (IQR 11-23) and 5746 words (IQR 3508-8626), with substantial variability. Industry-sponsored trials had significantly longer SIS/ICFs than academic trials (mean difference + 8.1 pages, p < 0.01). German SIS/ICFs were on average 4.4 pages longer than Austrian SIS/ICFs (p = 0.018). Exploratory analyses suggested that formatting choices, repetition, and expanded data protection sections contributed more to length differences than content allocation or readability, thus indicating that the main drivers of SIS/ICF length are modifiable in nature. These findings underscore the need for further research into the factors influencing document length, their implications for trial participants and how a further harmonization throughout the EU can be achieved for country-specific documents.