👉 In statistics and research design, a confounder is an independent variable that influences both the effect of another independent variable on the outcome of a study. In other words, it is an unknown factor that may affect both the treatment or the response variable. Confounders are often used in observational studies to prevent bias when comparing groups with different characteristics. For example, if you want to compare two groups based on different demographic factors (e.g., age, gender), confounding could be a key factor in