Noise: A Flaw in Human Judgment

by Daniel Kahneman

One underwriter we interviewed described her experience in becoming a veteran in her department: “When I was new, I would discuss seventy-five percent of cases with my supervisor.… After a few years, I didn’t need to—I am now regarded as an expert.… Over time, I became more and more confident in my judgment.” Like many of us, this person had developed confidence in her judgment mainly by exercising it. The psychology of this process is well understood. Confidence is nurtured by the subjective experience of judgments that are made with increasing fluency and ease, in part because they resemble judgments made in similar cases in the past. Over time, as this underwriter learned to agree with her past self, her confidence in her judgments increased. She gave no indication that—after the initial apprenticeship phase—she had learned to agree with others, had checked to what extent she did agree with them, or had even tried to prevent her practices from drifting away from those of her colleagues.