In the year 2005, the outbreak of a new disease affecting cattle had a devastating impact on the farm's dairy industry across the world. Known as 'whooping cow disease', fear of the virus quickly spread throughout the world causing people to avoid consumption of cattle and cattle related products such as dairy goods. How do you think this virus would affect chocolate sales? At the same time, certain brands of chocolate do not use milk in their production. How do you think their sales will be affected compare to the brand assigned to you?

Refine the model you created in previous questions by adding a dummy variable to represent the one-off occurrence of 'whooping cow disease'. In other words, estimate the following: