Book Review: ‘Partial Truths: How Fractions Distort Our Thinking’ By James C. Zimring

In the 1980s, media attention settled on the dangers of an immensely popular roleplaying game, Dungeons and Dragons, as a new cause of psychosis and suicide among teenagers. The evidence was hard to ignore. A rash of teenagers who played D&D had committed either suicide or homicide. The CBS news show 60 Minutes dedicated an entire hour to the D&D emergency and made the following statement: “There are those who are fearful that the game, in the hands of vulnerable kids, could do harm; and there is evidence that seems to support that view.”

And yet there was no real D&D emergency. This is because:

· In 1984, the suicide rate among U.S. teens was roughly 120 per one million per year, or .012 percent.

· Roughly three million American teenagers had played D&D. Over the course of several years, only 28 of them (.00093 percent) had killed themselves or someone else.

· This means that D&D players became fatally violent at a far lower rate than the average American teen.

Indeed, just looking at the math, one might suspect that D&D exerted a large protective effect on American teens. The CBS news producers missed that nuance, however. Like many of the panicking mothers, fathers, and school nurses and administrators, they failed to recognize the fractions that were crying out to be recognized and used.

Author James C. Zimring is the Thomas W. Tillack Professor of Experimental Pathology at the University of Virginia School of Medicine. In Partial Truths: How Fractions Distort Our Thinking, he presents the D&D quagmire as well as a bevy of sometimes frightening, sometimes charming examples of mathematical ignorance. One involved the storied McDonald’s and A&W rivalry. McDonald’s quarter-pounder had been a runaway hit since 1971. In the 1980s, A&W hoped to best McDonald’s by offering their customers even more meat — a 1/3 pound hamburger. “Third is the Word!” announced the advertising. However, “3” is a lower number than “4,” which made “1/3” seem smaller to many people than “1/4.” Who wants a smaller burger? A&W’s One-Third Burger was a decisive flop.

Despite its subtitle, Partial Truths: How Fractions Distort Our Thinking isn’t only a compilation of anecdotes. It’s also a treatise on how our minds fractionate the world with cognitive habits that create biases and thwart good decision-making.

Dr. Zimring argues that fractionated thinking misinforms our criminal justice system and impairs our altruism. He suggests that it helps create national belligerence and war-making. It drives divisive approaches to spirituality. And, in the Covid-19 pandemic, it has allowed many people to fall prey to conspiracy theories that have killed them and the people they love.

“For those of us lucky enough to be active members of a democracy, it seems a dereliction of our duty to not be an informed citizen …. Maybe we can habituate the metacognitive skills to recognize when we are misperceiving the fraction and when others are manipulating it … and clean up the parts we have wrong or find the parts we are missing. If not, perhaps we can decrease our confidence in our observations and beliefs, because we know we don’t know the whole story and we may have part of the fraction wrong.”

Also the author of What Science Is and How It Really Works, Dr. Zimring even teases apart evolutionary reasons for why our tendency toward error-prone cognition didn’t kill off our species ages ago. Partial Truths is a book to read through very carefully and then keep next to your desk, maybe alongside a fifth grade math textbook. Hey, let’s all keep help like that close at hand at least until the next time our prejudices are about to make us decide wrongly or vote stupidly.

Columbia University Press, Hardcover $27.99 (256 p) ISBN 978021554077. Also available as an e-book. Pub date May 2022.