Health care and its availability are important drivers of public health, but everyone knows behavior is a big deal, too. Over the past 50 years, Americans have quit smoking, started driving safer cars, put on weight, and bought more guns.
To make this cool chart, Susan Stewart of the National Bureau of Economic Research and David Cutler of the Harvard Department of Global Health and Population tallied up all the behavioral trends and summarized them. You can read the details of how they put it all together here.
One thing to note is that even though the decline in automobile deaths has been relatively modest, the increase in automobile safety has been enormous. The issue is that it's been partially offset by a huge increase in the number of miles driven per capita — "fatalities would have risen by over 200 percent if deaths per mile driven had remained constant," they write.
The smoking/obesity tradeoff is also worth keeping in mind. As many of us who used to smoke heavily know, you tend to put on weight when you quit. The public health impact of growing obesity has been serious and negative, but on net, the obesity problem is a less harmful one for the country's health than our former smoking problem.