Influential point

An influential point pulls the least-squares line noticeably toward itself, so dropping it shifts the fit by a lot. Points with extreme x-values, called high-leverage points, tend to be the most influential, often more than a point that is simply a vertical outlier. For example, one house priced far above the rest at a large size can tilt the whole price-versus-size line. You check for influential points by refitting the line without the suspect point and comparing the slope and correlation.