Does telling a consumer a product is on sale increase the likelihood that the consumer will buy the product? Over four months, new customers that enter a car dealership and ask to see a particular model of vehicle are randomized to one of two groups. The first group is simply quoted the retail price of the vehicle. The second group is told the vehicle is being offered at a reduced price for a special one-day sale before being quoted the retail price. Both groups are helped by the same sales associate, and the proportion of customers who request to buy the vehicle the same day is then compared between the two groups. What type of study is this?