RESUMEN
BACKGROUND: Elements of informed consent including capacity, disclosure, understanding, voluntariness, and permission of the participant, are all crucial for clinical trials to be legally and ethically valid. During the informed consent process, the patient information leaflet is an important information source which prospective research subjects can utilize in their decision-making. In the adequate provision of information, KGCP guideline necessitate 20 specific items, as well as the use language that individuals can understand. This study measures the vocabulary level of patient information leaflets in an effort to provide an objective evaluation on the readability of such material. METHODS: The word difficulty of 13 leaflets was quantitatively evaluated using Kim kwang Hae's vocabulary grading framework, which was compared to the difficulty level of words found in the 6th grade Korean textbook. The quantitative outcomes were statistically analyzed using chi-squared tests and linear by linear association for ordinal data. RESULTS: There was a statistically significant difference between the vocabulary level and frequency of words in leaflets and the 6th Korean textbook. The leaflets were on average 260 sentences and about roughly 15 pages long, including lay language (easier or equal to language used in primary school) of around 12% less; technical language of around 4.5% more. As the vocabulary grades increase, there was a distinct difference in vocabulary level between Korean textbook and each information leaflet (p < 0.001). CONCLUSION: Patient information leaflets may fail to provide appropriate information for self-determination by clinical trial subject through the difficulty level of its wording. Improvements in the degree of patients' understanding and appropriate use of information leaflets are collaboratively equipped to strengthen patient's autonomy and therefore guaranteeing participant's rights.