Prices of second-hand cars

Use this diagram to discuss the idea of the strength of a relationship between two variables.

Use the slider to adjust the strength of the relationship. The pop-up menu changes the 'explanatory' variable from one that is positively related to car price (engine size) to one that is negatively related (age).

Drag over the scatterplot to select slices. Explain that when the relationship is strong, the range of prices is small for any value of the explanatory variable so the explanatory variable would lead to accurate predictions.