The Myth of the Bell Curve

To Be different, We Have To Think differently

To combat violent gun crime in Cincinnati, police worked with Professor Tamara Herold from 2015 to 2016 to focus on the most violent locations. They relied on information from undercover informants, community partners, and surveillance to analyze what factors contributed to gun violence. Based on their findings, they changed the environment: installed streetlights, eliminated street parking because that’s where drug deals happened, demolished blighted buildings, and mowed tall grass that provided a place to hide ammunition. This ““pilot micro-location program” reported a drop of more than 80 percent in the number of shooting victims,” writes Amy Brittain for The Washington Post. Even though the method was a success, it is only used in four locations because the police department doesn’t have the resources to implement the strategy city-wide. Cincinnati suffered from a “record number of homicides in 2020,” explains Brittain.

Crime doesn’t happen in a uniform pattern across a city. Instead, it follows the Pareto Principle, where a few people are the perpetrators. A small percentage of residents cause the majority of the crimes. It is commonly known as the 80/20 rule, according to which 20% of the actors are responsible for 80% of the consequences. Italian economist Vilfredo Pareto noticed that 20% of Italy’s population owned 80% of the land in 1906. So, this ratio popped up in his garden, where 20% of the pea pods had 80% of the peas. The Pareto Principle occurs in the business world, where 20% of customers often generate 80% of sales. It also happens in the bird world: 80% of birds seen over a 13-year study in New York state only represented 20% of the total species seen in the study area.

The Pareto Principle contrasts with the Gaussian or bell curve way of thinking. In a bell curve world, 70% of the total bird species would have been seen in the study, as if all of the bird species were equally distributed across the sky. 70% of people would be the perpetrators of crime, and 70% of customers would account for the bulk of sales. However, that is not what happens in the bird world, the business world, or our society. Rather, the outliers—the select few people, animals, events, and customers—are the ones that have the most impact. This is also called the power law, which describes the relationship between the variables in the Pareto Principle ratio. In Figure 12, you can see how the power law graph has a long tail. At the skinnier end of the tail are the few individuals with the most impact, compared to the bell curve graph, where impact is distributed across a larger chunk of individuals.

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Figure 12: A Pareto Distribution vs. a Gaussian Curve. From “We Need to Let Go of the Bell Curve” by Adrian Gore for Harvard Business Review.

When a variable changes in the power-law graph, it has a multiplicative shift on the other variable—a large impact. For example, in a diversified internet marketplace full of sellers who each make niche products, when one new customer buys something, that business’s revenues may go up by 30%. In comparison, if a customer walks into a Walmart full of mass-appealing products, that person’s t-shirt purchase is lumped into the middle of the bell curve. It is additive rather than multiplicative. The niche market is geared toward power-law distribution, while the mass market is geared toward Gaussian or bell curve distribution.

Even though humans think the world functions around averages like the bell curve, “most human activities, as well as many disciplines—from physics and biology to linguistics, finance, and computer science—follow a Pareto distribution,” explains Adrian Gore for Harvard Business Review. Our world is made up of people, animals, and systems that relate to each other in complex ways. One action does not cause a single reaction; it creates a multiplicative effect, like the butterfly effect. When a volcano erupts, myriad impacts with far-reaching consequences through space and time result. Power-law distribution, or the Pareto Principle, speaks to the interrelatedness of our intricate world.

Dr. J. Bruce Stewart

47 articles

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Part 2 of this article will discuss the application of the Pareto Principle to DEI and the elimination of racial bias.

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