Answer: To work out a residual, you must take the predicted value and subtract it from the measured value.
Explanation:
A residual plot is a graph that shows the residuals on the vertical axis and the independent variable on the horizontal axis. To find a residual you must take the predicted value and subtract it from the measured value.
Its values should be equally and randomly spaced around the horizontal axis. If the points in a residual plot are randomly dispersed around the horizontal axis, a linear regression model is appropriate for the data; otherwise, a non linear model is more appropriate.