A few interesting tidbits...I just read the study from above. The journalist who wrote the article came up with the $78 billion based on their data, but it didn't come from the researchers. I think he misrepresents some of the study just a bit. That said, here are some interesting speculations from the researchers (all MDs, by the way).
These data came from 39 physicians who self-reported how defensive each of their orders were from the previous day. It was a 5-point scale ("not at all" to "completely" defensive).
2.9% of the costs were rated to come from "completely defensive" decisions and the highest percent was for diagnostic cardiology (about 15-17% by the chart) and "Other Diagnostic" (about 15%).
That said, the physicians who made made the most self-reported defensive decisions did not make any statistically significantly more orders than those who made fewer self-reported defensive decisions. They also spent less per patient (not a statistically significant difference, but the mean was less) than those who made the least defensive decisions.
They acknowledge that the ratings are subjective. I would also posit that doctors, who generally favor tort reform, are more likely to rate their decisions as being defensive.
Their conclusion:
"...although a large portion of hospital orders had some defensive component, our study found that few orders were completely defensive and that physicians' attitudes about defensive medicine did not correlate with cost. Our findings suggest that only a small portion of medical costs might be reduced by tort reform" (Rothberg, Class, Bishop, Friderici, Kleppel, & Lindenaure, 2014, p. 1868).