In observational research within clinical studies, where there is no invasive procedure or intervention on patients, and research is conducted using only information such as clinical data without obtaining samples from the human body, it is not always necessary to obtain direct consent from each individual patient. However, according to national ethical guidelines, it is required to notify or disclose information about the research, including its purpose, and to provide an opportunity for patients to refuse participation if they wish. This approach is known as "opt-out.