the manager of an ice-cream parlor decides to introduce a new ice-cream flavor in his dallas, tx based restaurants to compare the sales of these restaurants to the ones with no new flavors. she decides to run a difference in difference approach. which of the following is true?
(a) the first difference would be the difference in the sales of the dallas stores before and after the introduction
(b) the second difference would be the difference in the sales in other stores before and after the dallas stores introduced the new flavor
(c) the second difference would be the difference between the post introduction sales in the dallas stores and the control group
(d) only a& b