The word ''bias'' commonly appears in conversations about mistaken judgments and unfortunate decisions. We use it when their is discrimination, for instance against women or in favor of Ivy League graduates.

But the meaning of the word is broader : A  bias is any predictable error that inclines your judgment in a particular direction. For instance, we speak of bias when forecasts of sales are consistently optimistic or investment decisions overly cautious.

Society has devoted a lot of attention to the problem of bias - and rightly so. But when it comes to mistaken judgments and unfortunate decisions, there is another type of error that attracts far less attention : noise.

To see the difference between bias and noise, consider your bathroom scale. If on average the readings it gives are too high [or too low], the scale is biased.

If it shows different readings when you step on it several times in quick succession, the scale is noisy. [Cheap scales are likely to be biased and noisy.]  While bias is the average of error, noise is their variability.

Although it is often ignored, noise is a large source of malfunction in society. In a 1981 study, for example, 208 federal judges were asked to determine the appropriate sentences for the same 16 cases.

The cases were described by the characteristics of the offense [robbery or fraud, violent or not] and of the defendant [young or old, repeat or first-time offender, accomplice or principal].

You might have expected judges to agree closely about such vignettes, which are stripped of distracting details and contained only relevant information.

But the judges did not agree. The average difference between the sentences that two randomly chosen judges gave for the same crime was more than 3.5 years. Considering that the mean sentence was  seven years, that was a disconcerting amount of noise.

Noise in real courtrooms is surely only worse, as actual cases are more complex and difficult to judge that stylized vignettes.

It is hard to escape the conclusion that sentencing is in part a lottery, because the punishment can vary by many years depending on which judge is assigned to the case, and on the judge's state of mind on that day.

All judicial systems of the world are unacceptably noisy.

This Master Essay and its Publishing continues to Part 2. The World Students Society thanks emeritus professor of psychology at Princeton, Daniel Kahneman. He is also a recipient of the 2002 Nobel Memorial Prize in Economic Sciences.

And Olivier Sibony a professor of strategy at HEC Paris business school. And Cass R. Sunstein, a law professor at Harvard.

They are the authors of the forthcoming book ''Noise : A Flaw in Human Judgment,'' on which this essay is based.


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