Effect of a drug in reducing heart rate

Use this page to show that zero slope implies that there is no association between Y and X. Explain that this is an important special case of the model.

Adjust the model slope to β1 = 3.0
Heart rate decreases on average by 3 beats per minute for every extra mg of drug. Rotate to a display of density vs y (button at top right). Drag the slider to show how the heart rate distn depends on drug.
Adjust the model slope to β1 = 0.0
If this model is appropriate, the distribution of heart rate reduction is the same for all doses.

The context of the model is the effect of a drug (mg) in lowering the heart rate of adults. The response is the reduction in heart rate (before minus after receiving the drug) in beats per minute.