Harvard psychologist Gene Heyman says what while people may have predispositions to addiction, evidence shows people consciously choose to break their addictive habits (or not). In refuting the standard dictionary definition of addiction as something entirely compulsive and beyond our control, the comparison of addiction to a disease is untennable, Heyman says. He prefers the American Psychiatric Association's definition: continued use of a substance despite net adverse consequences. As evidence, he cites anecdotal reports of addicts who have considered their children or their parent's opinion of them as a reason to give up substance abuse. This kind of consideration is not available to those have more literal diseases like cancer.