Chapter 7: Single-Case Designs
Imagine that you’re the director of a food bank. For the last two years you have placed containers in a grocery store in town where shoppers can leave donations of food as they leave the store, but your agency has never tracked the donations there. Now, though, as the economy worsens and unemployment rises in your community, your agency is unable to keep up with the need for food, so you resolve to increase the donations you receive at this grocery store. Your objective is to get $1,500 a week in donations from this grocery store. So, with the cooperation of the grocery store, you implement an intervention designed to achieve this objective. The intervention involves prompts using point-of-sale reminders (signs located on the shelves urging shoppers to buy nearby items for donation), and it was inspired by research reported by Farrimond and Leland (2006).
This chapter describes and discusses the use of single-case designs. We begin with the basic A-B design, since understanding and using other single-case designs is not complicated once the A-B design is mastered. We also discuss the idea of causation in single-case design and some of the errors that can be made in drawing conclusions about the effectiveness of interventions. Finally, we discuss a number of designs, such as A-B-A-B, several types of multiple baseline designs, and others.