Selection bias occurs when the participants included in a study or analysis are not representative of the larger population. This can lead to skewed results and conclusions that do not accurately reflect the true situation. For example, if a survey about health habits only includes responses from gym members, it may overlook the behaviors of those who do not exercise regularly. This bias can arise from various factors, such as how participants are chosen or self-selection, where individuals opt to participate based on certain characteristics. Addressing selection bias is crucial for ensuring the validity of research findings and making informed decisions based on accurate data.