Model Evaluation

A residual value measures how much a regression line vertically misses a data point. Regression lines are the best fit for a set of data. We can think of the lines as averages; a few data points will fit the line, and others will miss. A residual plot has the residual values on the vertical axis, and the horizontal axis typically displays the independent variable.

Residual scatterplot

The scatterplot below (residual values against y_hat predictions) is helpful for understanding randomness.