Doctors’ subtle social cues transmit expectations of efficacy to patients


Doctors transmit their expectations about the efficacy of a treatment to patients via subtle social cues that exert a substantial placebo effect on outcomes, new research shows.

While the influence of doctor and patient expectations on responses to treatment has long been recognised and led to ‘double blinding’ in controlled trials, there has been surprisingly little research into how provider expectations influence clinical outcomes, according to US psychologists.

Therefore in an elaborate series of experiments, researchers at Dartmouth College created a series of simulated doctor-patient encounters in which they measured perceptions of the analgesic efficacy of a placebo cream ‘thermedol’ against heat-induced pain.

Using 194 students in doctor and patient roles, they first fooled the ‘doctors’ into believing they had an active analgesic cream by secretly using a lower temperature thermal stimulus in half the patients.

In a subsequent set of single blind experiments they found that the ‘doctors’ who believed they were using an active analgesic transmitted this expectation to their patients. When doctors thought they were using thermedol, their patients reported a higher expectation of treatment success. Furthermore, the ‘patients’ had lower pain scores when heat was applied to the skin compared to patients treated by the same cream but which the doctor thought was a placebo.

These subjective effects were backed up by objective measures of patient’s facial expressions of pain and by autonomic arousal (skin conductance).

Reporting their findings in the journal Nature Human Behaviour, the researchers noted that doctors who believed they were using an active analgesic treatment also got a higher rating for perceived empathy from their patients. The doctors’ expectations of treatment success also manifested as subtle differences in their facial expression behaviours during the clinical consultation, particularly when they knew they were using a placebo.

“Doctors appeared to convey more information relating to facial displays of pain when administering the control treatment, which they believed was ineffective.

“We speculate that there are at least two possible mechanisms underlying the socially transmitted placebo effect. One possibility is that the doctors send some nonverbal information that communicates their beliefs about which treatment is more likely to be the active treatment. Alternatively, the doctor might be more attentive to the patient and develop a more empathetic connection which ultimately makes the patient feel better when they are receiving pain stimulations. The patient may then incorrectly attribute this analgesic effect to the thermedol treatment.”

The researchers said their finding have “important implications for virtually all clinical interactions between patients and providers and highlights the importance of explicit training in bedside manner when delivering information and interventions.”

“For example, some trainings focus on providers’ psychological aspects, such as empathy and others emphasise communication skills.

“We believe that the tremendous resources invested in discovering new treatments should be complemented by additional investment in understanding the mechanisms underlying one of the oldest and most powerful medical treatments—healers themselves,” they concluded.

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