The logic seems obvious. Free health care means better health. Needy or elders can afford healthcare because they are subsidized by the federal government. After they are not ill, they become more productive, and then wealthier, and then escape from the poverty trap. But, this logic is dead wrong.
What is wrong? This assumption is fatally wrong: free health care does not improve health.

What makes these research great? Because this is the first large scale randomized trial controlled research ever conducted to address this important question. Many research has replicated this method and found similar result.