Following implementation of a new city law, a restaurant chain began displaying the nutrition labels for their menu items.

Following implementation of a new city law, a restaurant chain began displaying the nutrition labels for their menu items. The restaurant owner recorded sales of the 15 highest-calorie menu items on three occasions—once the month before the change in menu display, once the week of the change in menu display, and once the month after the change in menu display. The owner observed that the sale of the high-calorie menu items dropped, while overall sales remained steady. What is the dependent variable in this study?