Second Opinions: How Should You Choose?

Dov Michaeli

Posted 5/9/12 on The Doctor Weighs In

Incredulous Dov

I have frequently been asked to render judgment on another doctor’s diagnosis, or treatment plan. Other times I am asked anxiously: “should I get a second opinion”? The implicit assumption in this sort of questions is that “two heads are better than one.” Or stated more broadly, we put our faith in the “wisdom of the crowd,” whether the “crowd” is made up of two or two-thousand individuals.

I have to admit I’ve had some nagging doubts about this all-encompassing wisdom. For instance, wisdom of the crowd has been amply documented in estimation tasks (“how many people in this crowd?  What is your estimate of the completion date of the project?”). The reason this works is that it exploits the benefit of error cancellation; the outlier estimates on either side cancel out each other and we end up with the consensus opinion, that is closest to the truth. But how do you decide when the issue is not quantitative? Think of the virtually unanimous opinion of the White House crowd to go to war in Iraq. Where was the “wisdom” there? More interesting, we could drill deeper and ask why is it that the crowd reached such a wrong decision? Wisdom of the crowd was hailed as a source of near-magical creativity and unparalleled wisdom and forecast accuracy. Some of these attributions have proved to be unfounded. For instance, with respect to creative potential, groups that engage in brainstorming lag hopelessly behind the same number of individuals working alone. The key to benefiting from other minds is to know when to rely on the group and when to walk alone. Wouldn’t it be nice if we had some sort of an algorithm to guide us in making this decision?

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