This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Other Key Definitions & Concepts, Subject name: Social & Preventive Medicine
[{'content': "Expectation of life, free of disability is known as:- \nSelect and explain. \nA. Park's index, B. Smith's index, C. Sullivan index, D. Life index", 'role': 'user'}, {'content': "Answer: C \nExplanation: Sullivan's index is defined as Disability free life expectancy (DFLE). Sullivan's index = Life expectancy -- duration of disability.", 'role': 'assistant'}]