Evidence based medicine is first and foremost at the Preventing Overdiagnosis Conference in Dartmouth this week. The importance of data, research, and careful analysis has been repeatedly hammered home, with talks catchily entitled such as, “Does inclusion of  total cholesterol in mortality risk algorithims lead to overestimation of risk?” “Ten years prospective data from the Norwegian HUNT 2 Study,” and “Impact of computer aided mammography dissemination on early-stage breast cancer treatment rates in the Medicare population.”

And so say all of everyone present. You won’t find many dissenters here. Indeed, the likelihood is that you won’t find many dissenters anywhere—what sort of doctor wouldn’t support evidence based medicine? Well done all of us.

So with that in mind, why is overdiagnosis so prevalent? A lot of the usual bogey men are being flagged up here—those damn pharma execs and their misleading marketing, the shoddy media and their inability to understand science or straight up desire to sensationalise it, the fee for service model in so many systems that allows doctors (“other doctors, not me, you understand”) to line their pockets.

But a recurring theme from the floor that does not feature in many talks is fear. And, in particular, the fear of getting sued.

At almost half the sessions I have attended now, the audience has applauded the data, nodded at the wisdom of the speaker, acknowledged the flawless analysis of the situation, and at some point confessed that when the patient is in front of them, the fear of being sued can override everything. So just to be safe, they will order the extra test or prescribe the extra treatment. That anecdote of a colleague or doctor in the newspaper has the ability to instil a fear that overpowers all rational judgement.

And fear is indeed a powerful motivator. It’s not a beneficial motivator, it’s often not evidence based, and it rarely includes careful assessment of the data, but it is undeniably powerful.

And moreover it is frequently driving patient behaviour as well. Those damn pharma marketing campaigns mentioned above are not designed to appeal to a patient’s logic, but their fear of disease—do you have these symptoms? Then you might have CANCER!!! So when a patient presents with a lump on her breast, she’ll probably want to know what it is at some point, but the first thing she will want to know is if it’s cancer and if she is going to die.

In so many consultations the elephant in the room is not disease, diagnosis, or treatment, but fear. And what is emerging at this conference is that the fear of both patient and doctor can sometimes override the best knowledge, research, and information known to man.

As Franklin D Roosevelt hypothesised in his first inaugural address—perhaps the thing we have to fear is fear itself, “nameless, unreasoning, unjustified terror which paralyzes needed efforts to convert retreat into advance.”

Edward Davies is US news and features editor, BMJ.