You may have missed this when it first appeared.

Experts from Harvard and the University of Southern California say assumptions made by some analysts that defensive medicine is not an important facet of the high cost of healthcare may be wrong.
Those assumptions were based on data showing that malpractice reforms instituted in some states did little to reduce healthcare spending. 
According to the report from the National Center for Policy Analysis about an article in the wall Street Journal, defensive medicine ("ordering some tests or consultations simply to avoid the appearance of malpractice") is just as common in states with low as it is in those with high malpractice risk. In fact, about 2/3 of doctors in both the low and high risk states admitted to practicing defensive medicine.
My experience is that the 2/3 figure is probably a very low estimate. Just about every physician I know has  ordered a test or consult strictly to "cover his/her ass" if something were to go wrong. I am certain it happens tens of thousands of times per day in the US.

I can cite many examples of defensive medicine. Here are a few.

A young man with chest pain arrives in the ED. After taking a history and examining the patient, the ED MD is 99.99% certain that the patient did not have a heart attack or a pulmonary embolism. But he's a little short of breath. He remembers a case of a fatal PE with only minimal shortness of breath, orders a blood gas and CT angiogram of the chest.
A young girl comes in with lower abdominal pain, no GI symptoms, no fever. The pain improves over a couple of hours. Could she have appendicitis? Very doubtful, but yes, it is possible. Will she get a CT scan or an ultrasound? Yes. People who get sent home from EDs and return with appendicitis often have complications. Complications = lawsuit (delay in diagnosis).