Residual plot

A residual plot helps you judge whether a linear model is appropriate by spreading the leftover errors out for inspection. Random scatter with no pattern around the horizontal zero line suggests a line fits well, while a curved or fanning pattern warns that it does not. For example, a U-shaped residual plot signals the true relationship is curved, so a line understates it at the ends. You read residual plots for both curvature and changing spread before trusting a regression.