Kroger, a grocery store chain, wants to identify the ideal store layout for increasing store sales. Because it primarily uses two store designs, one a grid layout with vertical aisles divided by a center aisle and another using a traditional straight-aisle pattern, Kroger will match pairs of stores that have different designs but similar shopper demographics and location. Sales from each pair will then be compared to determine if store design is related to sales. Which type of study is this an example of?