Regression Diagnostics: Leverage & Cook's Distance (2D)

A regression line's coefficients are averages, but they aren't democratic — a single point far from the center of the data can steer the fit far more than the rest of the cloud combined. This simulator renders an ordinary-least-squares scatter across three linked 2D panels: the fitted line itself, a live bar chart of each point's Cook's distance, and a leverage-vs-standardized-residual diagnostic with iso-Cook's-distance contours. Drag points around or inject a deliberately extreme outlier and watch all three panels update together, so you can see exactly why a point is or isn't influential, not just that it is.