Anyone seeking medical care for a serious illness wants certainty in their diagnosis and treatment. The unsettling message of Random Acts of Medicine: The Hidden Forces That Sway Doctors, Impact Patients, and Shape Our Health, however, is that those understandable desires are often undermined by pure chance.  In their revealing book, Harvard Medical School professor and economist Anupam B. Jena and critical care physician and health care policy researcher Christopher Worsham rely on natural experiments—studies based on collecting and analyzing data from random events occurring in the real world instead of controlled environments—to illustrate the role that randomness plays in America’s health care system. It’s a system that, in 2019 alone, spent $3.8 trillion—17.7% of the United States’ gross domestic product—and yet is “inefficient, inequitable, and poorly performing compared with other wealthy nations,” they write. Jena and Worsham report on numerous studies, some of which they helped conduct, that attempt to answer some vexing questions: Why do children born in the fall have markedly higher influenza vaccination rates than their counterparts with summer birthdays? Why, despite similar conditions, are some patients more likely than others to receive an opioid prescription in the emergency room and maintain that prescription long after they’ve returned home? Why is an obstetrician more likely to perform an unplanned cesarean section if their previous patient’s vaginal birth presented complications? The answers, they argue, can provide critical insights into how to improve the quality of health care. The book’s sometimes whimsical chapter titles conceal serious findings. “What Happens When All the Cardiologists Leave Town?” examines the survival outcomes for high-risk cardiac patients who are hospitalized during the annual professional conference for interventional cardiologists, versus those treated when those same cardiologists are back home. “What Do Cardiac Surgeons and Used-Car Salesmen Have in Common?” considers “left-digit bias,” a cognitive blind spot Jena and Worsham believe explains the differing care patients with heart attack symptoms who are just under 40 sometimes receive compared to those who have recently passed that milestone.  If these unexpected insights sound familiar to readers of books like Malcolm Gladwell’s Outliers, there’s a reason. In addition to his professional duties, Jena hosts the podcast “Freakonomics, M.D.,” where he explores similar behavioral economics issues. Though their tone is occasionally lighthearted, he and Worsham repeatedly drive home a serious point: The American health care system is failing to deliver optimal care, often due to the unquestioned assumptions and inherent biases of its providers. If this provocative book can spark conversations about how to examine these persistent problems with fresh eyes, its authors have accomplished something truly important.