Noise: A Flaw in Human Judgment

by Daniel Kahneman

wherever there is judgment, there is noise—and more of it than you think.

In 1973, a famous judge, Marvin Frankel, drew public attention to the problem.

A study of thousands of juvenile court decisions found that when the local football team loses a game on the weekend, the judges make harsher decisions on the Monday (and, to a lesser extent, for the rest of the week). Black defendants disproportionately bear the brunt of that increased harshness.

When the guidelines were mandatory, defendants who had been sentenced by a relatively harsh judge were sentenced to 2.8 months longer than if they had been sentenced by an average judge. When the guidelines became merely advisory, the disparity was doubled.

After the Supreme Court’s decision, there was a significant increase in the disparity between the sentences of African American defendants and white people convicted of the same crimes. At the same time, female judges became more likely than male judges were to exercise their increased discretion in favor of leniency. The same is true of judges appointed by Democratic presidents.

Most of us, most of the time, live with the unquestioned belief that the world looks as it does because that’s the way it is. There is one small step from this belief to another: “Other people view the world much the way I do.” These beliefs, which have been called naive realism, are essential to the sense of a reality we share with other people.

We have little opportunity to notice that our agreed-on rules are vague, sufficient to eliminate some possibilities but not to specify a shared positive response to a particular case. We can live comfortably with colleagues without ever noticing that they actually do not see the world as we do.

Consider another mechanism that many companies resort to: postmortems of unfortunate judgments. As a learning mechanism, postmortems are useful. But if a mistake has truly been made—in the sense that a judgment strayed far from professional norms—discussing it will not be challenging.

System noise is inconsistency, and inconsistency damages the credibility of the system.