Weapons of Math Destruction Summary

Weapons of Math Destruction is a book by Cathy O’Neil that examines the dangers of using “Big Data” to make decisions that can alter the course of people’s lives.

  • “Weapons of Math Destruction” (or WMDs) are Big Data models that use algorithms to make decisions. WMDs ignore nuance and often rely on flawed data.
  • Many WMDs are opaque to the people whose lives they affect, yet they are everywhere: in finance, college admissions, advertising, police departments, the job market, politics, and social media.
  • O’Neil concludes that the use of WMDs is biased, careless, and ultimately unethical.


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Last Updated on August 14, 2019, by eNotes Editorial. Word Count: 1239


Cathy O’Neil’s nonfiction book Weapons of Math Destruction exposes how data collection is being used to undermine individuals’ right to privacy and the democratic society in which we live. Weaving her personal experiences with research, O’Neil traces the development of big data and its far-reaching impacts on the average citizen.

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Plot Summary

In the introduction of the book, O’Neil describes her lifelong love for numbers, explaining how this led to a career in the field of mathematics. After the housing crisis and economic downturn of 2008, however, O’Neil recognized that mathematical equations were not infallible in measuring human behavior. She explains how, after 2010, the public accepted the growing trend of corporations and public services using algorithms to dictate much of their lives.

She cautions, however, that the ubiquity in these algorithms does not mean they are harmless. To illustrate this, she discusses the educational reforms in Washington, DC, under Michelle Rhee, whose teacher evaluation system IMPACT was meant to identify the lowest-performing teachers in the school district using math. Instead of solving the district’s student achievement problem, the system fired good teachers based on a number that was calculated using undisclosed methods and unreliable data. The ability of mysteriously guarded algorithms to upend an individual’s life without much proof is what inspires O’Neil to write about this subject.

In “Bomb Parts: What Is a Model?” O’Neil discusses how statistical analysis became integral to the sport of professional baseball. She suggests that baseball’s use of data to analyze players’ performance serves as a contrast to the destructive power of weapons of math destruction (WMDs) because it is transparent. In the rest of the chapter, O’Neil explains how models are created with goals and ideology in mind, which means they are just as biased as the people who create them. Because of this, O’Neil asserts that it is dishonest and immoral to keep the details of the model’s creators and purpose from the people whose lives the model will impact. O’Neil discusses recidivism models in prisons as an example of how models can have detrimental consequences, even if they are unintended.

In the next chapter, “Shell Shocked: My Journey of Disillusionment,” O’Neil goes into detail about how she arrived at her suspicions about Big Data. In her time working in hedge funds, O’Neil witnessed the havoc that models and algorithms could wreak on the economy during the 2008 financial crisis, not to mention the human suffering this caused. After leaving Wall Street, O’Neill worked in e-commerce, calculating the likelihood of website visitors to buy products. Even still, O’Neil grew increasingly uncomfortable with the way numbers were being used to manipulate, quantify, and control people—leading her to use her mathematical prowess to lead the charge in investigating Big Data.

In the next chapter, “Arms Race: Going to College,” O’Neil explains how US News undertook the task of ranking the nation’s colleges and universities based on a complex system of mathematical...

(The entire section contains 1239 words.)

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