Layne Is Trying to Watch Less Television

Essay

Layne is trying to watch less television. Her friend Ryan is a psychologist who agrees to help her. He creates a treatment plan that involves giving Layne $5 for every day that she watches fewer than 90 minutes of television. He monitors her television watching for 3 days, treats her for 3 days and monitors her, and then just monitors her for 3 more days.
What type of design is Ryan using to change Layne's behavior? Name a threat to internal validity that this design is well suited to address.