The technique used by Joseph to treat Joanna is Token Economy.
People who exhibit desired behaviors are rewarded with tokens, such as money or points, under the concept of the token economy, a type of behavior therapy. This system of rewards can be used to motivate individuals to alter their behavior and improve beneficial behavior, including weight loss. In this instance, Joseph is using a reward system to encourage Joanna to lose weight by rewarding her for each pound she loses.
Token economies are based on the principles of applied behavior analysis and emphasize the use of positive reinforcement to influence behavior (ABA). Children can learn to self-regulate their behavior, understand delayed reinforcement, and make progress by using token economies.
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