An experiment was conducted to test the effects of coupon value on redemption. Personal interviews were conducted in New York with 280 shoppers who were entering a supermarket. These shoppers were given a coupon for one of four brands prior to entering the store. Two coupon values were used, one offering 15-cents off and the other 50-cents off. Shoppers were randomly assigned to these two coupon-value levels. Four brands — Tide detergent, Kellogg's corn flakes, Aim toothpaste, and Joy liquid dishwashing detergent — were used. These same shoppers were re-interviewed upon leaving the store and asked to report on any coupons used in the store. What is the dependent variable in this experiment?