A case series is a type of research study design in which a small group of individuals who have a similar condition or experience are examined and reported on. This type of study typically involves descriptive analyses of a series of cases, without any control group for comparison. Case series are often used in medical and clinical research to provide detailed insights into rare diseases, new treatments, or unique patient experiences. They can help researchers identify patterns, trends, and potential associations that may warrant further investigation in larger, more rigorous studies. Case series can be a valuable tool for generating hypotheses and exploring new avenues of research, but they are limited in their ability to draw definitive conclusions about cause and effect relationships due to their observational nature.