He videotaped the parents talking with their doctor about vaccines during a routine well-child visit. The doctors, he noticed, handled the conversation in one of two ways.

The first, Opel calls “presumptive.”

“The doctor,” he noticed, “just simply presumed that the parent was going to be fine with the vaccines that the doctor was going to recommend,” saying something like ” ‘So, Johnnie’s due for DTaP and Hib today’ – period. Move on.”

Some other doctors, Opel observed, invited parents to discuss their feelings about vaccines — “sort of invoking a shared decision-making approach, inviting the parent to be part of this conversation.” These doctors, he says, were more likely to ask, ” ‘So, Mom: What do you want to do about vaccines today?’ ”

The study’s surprising results: When doctors assumed parents would be OK with vaccines, they were. More than 70 percent had their child vaccinated.

On the other hand, when physicians were more flexible and allowed for discussion, most of the parents — 83 percent — decided against vaccination.