Im having some trouble figuring out this question from my ho

I\'m having some trouble figuring out this question from my homework:

True, False, Uncertain with Explanation:

4. In the above regression, I should also include variables for whether or not each store is running a sale. Otherwise, omitting that variable will bias my coefficient estimates on weather conditions

Solution

Yes. you should include that variable that whether or not each store is running a sale. otherwise it may become a spurious correlation for some cases. As it may happen that there may exist a very high positive correlation between effect of weather on sales but the store is not running a sale at all. then the prediction about the future sale would be false and the correlation would be spurious.