Effectiveness, Quality & Performance: What's the Difference?

Thomas McLellan, PhD

Addiction, Service Delivery

October 2010

Dr. Thomas McLellan, Director at the Center on Substance Abuse Solutions at the University of Pennsylvania, describes the difference between three commonly misused terms: effectiveness, performance, and quality. He argues that effectiveness is about outcomes while performance is about functioning, and good treatments without follow-up might be misunderstood as poor treatments rather than incomplete treatments. He provides two compelling examples of such a misunderstanding.

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