Outliers are extreme values in data that can mess up statistical analysis. They can mess up estimates and make errors more likely. Researchers often don't check for outliers, but they can really mess things up. Outliers can come from mistakes in recording data, lying, or just random chance. There are three types of outliers: Point, Contextual, and Collective. Robust regression is a good way to find and deal with outliers in data. It gives different results than regular regression when outliers are present.