Allen B. Downey, "Probably Overthinking It: How to Use Data to Answer Questions, Avoid Statistical Traps, and Make Better Decisions" (U Chicago Press, 2023)

Oct 10, 2025

Allen B. Downey, a principal data scientist and author, delves into the importance of statistical thinking and its real-world applications. He uncovers the friendship paradox, highlighting how we often perceive ourselves as having fewer friends than our peers. Downey addresses sampling bias with concerning examples, such as inflated recidivism rates. He also critiques the 10,000-hour rule for expertise and explains how misinterpreting data has led to misleading policies. Overall, he emphasizes the need for better data literacy in society.

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INSIGHT

Data Can Clarify Or Distort Reality

Data can both clarify the world and mislead if we ignore selection effects and biases.
Allen Downey argues that statistical thinking helps reveal real causes and prevent distortions.

INSIGHT

Average Person Is Rare In Many Dimensions

In high dimensions, most individuals will deviate from the mean on some measures, so a single "average" person is rare.
Downey shows with 10 then 96 measurements that everyone is "weird" in some ways.

INSIGHT

Selection Bias Creates The Friendship Paradox

Sampling method changes observed distributions: selecting friends oversamples popular people and biases averages.
This "inspection paradox" explains why most people have fewer friends than their friends do.

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Statistics are everywhere: in news reports, at the doctor's office, and in every sort of forecast, from the stock market to the weather. Blogger, teacher, and computer scientist Allen B. Downey knows well that people have an innate ability both to understand statistics and to be fooled by them. As he makes clear in this accessible introduction to statistical thinking, the stakes are big. Simple misunderstandings have led to incorrect medical prognoses, underestimated the likelihood of large earthquakes, hindered social justice efforts, and resulted in dubious policy decisions. There are right and wrong ways to look at numbers, and Downey will help you see which are which.

Probably Overthinking It: How to Use Data to Answer Questions, Avoid Statistical Traps, and Make Better Decisions (University of Chicago Press, 2023) uses real data to delve into real examples with real consequences, drawing on cases from health campaigns, political movements, chess rankings, and more. He lays out common pitfalls--like the base rate fallacy, length-biased sampling, and Simpson's paradox--and shines a light on what we learn when we interpret data correctly, and what goes wrong when we don't. Using data visualizations instead of equations, he builds understanding from the basics to help you recognize errors, whether in your own thinking or in media reports. Even if you have never studied statistics--or if you have and forgot everything you learned--this book will offer new insight into the methods and measurements that help us understand the world.

Allen B. Downey is a curriculum designer at the online learning company Brilliant and professor emeritus of computer science at Olin College.

Gregory McNiff is a Managing Director in the New York office of the Blueshirt Group, an IR firm focused on technology. Greg holds an MBA from the University of Chicago Booth School of Business, an M. Litt. in Shakespeare Studies from the University of St. Andrews and a B.A. in Classical Languages from Columbia University.

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