Beyond Credibility: How Evidence Shows What Really Works Helen Pearson Princeton University. Press (2026)

Consolidating the use of evidence in health and public policy has required decades of challenging work. Fifty years ago, doctors used to think that babies should sleep on their stomachs, advice popularized by American pediatrician Benjamin Spock and others. It took a synthesis of observations and case studies to show that this was wrong: babies should sleep on their backs to minimize the risk of sudden infant death syndrome (SIDS). More than 50,000 deaths could have been avoided in the United States, Europe and Australasia if this evidence had been combined and put into practice sooner.

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Beyond that data, the randomized controlled trial (RCT) is often the gold standard for medical or public policy evidence. Including a control group with which to compare the interventions shows what would have happened without it. Combining many trials into a meta-analysis gives practitioners and policymakers more confidence about whether a drug or treatment works.

In Incrediblejournalist and science communicator Helen Pearson (who is editor of Nature) presents an accessible account of how such practices spread. Covering topics ranging from policing to child development, it focuses on outcomes that matter to everyone, whether it’s safer neighborhoods or better birth procedures.

This book is not a technical treatise, nor should it be. As researchers know, the details of RCTs soon become technical once their basic principles have been explained. But Pearson accomplishes a narrative feat. Anyone can read and enjoy the book, although there are details for experienced readers. The background investigation is impeccable. The only slip I noticed is the statement that “in 1964, about 25 out of every 1,000 children in the United States died from sudden infant death syndrome, or SIDS”; In fact, this figure is the rate of deaths from all causes, with SIDS being a small fraction.

Facing the facts

The book shares many examples of successes, where strong evidence has corrected long-accepted bad practices. A 2002 Women’s Health Initiative trial¹ showed that hormone replacement therapy (HRT), widely prescribed to prevent heart disease, according to previous observational studies²It actually increased the risk of cardiovascular disease and breast cancer.

Similarly, a systematic review of nine randomized trials³ Studies conducted between the 1970s and 1990s showed that an anti-crime program adopted by many US states was counterproductive in practice. Known as Scared Straight, the initiative involved sending children at risk of crime to prisons to talk to incarcerated people. But in the end, the participants were more likely to offend than those in the control group.

Pearson recounts horror stories from before the RCTs were implemented, including episodes in which doctors did not administer antibiotics to treat early-stage measles, as was taught in medical schools before six RCTs showed that the drugs prevented fatal complications. Furthermore, the two million arthroscopies performed each year worldwide were found to be largely unnecessary, given all the risk and cost involved, following a 2016 trial.⁴ showed that this surgery did not work any better than exercise therapy for treating torn knee cartilage.

Pearson has a good eye for the people involved and tells vivid stories about how some scientists who championed RCTs were treated as mavericks and faced resistance to their ideas. Medical and public policy professionals were often bothered by findings that challenged clinical judgment and professional autonomy.

These colorful characters include David Sackett, a “larger than life” American-Canadian pioneer of evidence-based medicine who rode a motorcycle while wearing a purple jumpsuit; Eric Barends, an advocate of evidence in management studies, who left his home in Leiden, Netherlands, to live in a converted bus that he shipped to California; and Lawrence Sherman, who joined the New York City Police Department as an investigator in 1971 and later invented evidence-based policing.

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Pearson devotes much space to women, including Esther Duflo, the second woman to win the Nobel Prize in economics; Judith Gueron, a social policy researcher who said the trials were “like tasting toothpaste” and combated sexism; and Denise Rousseau, public policy and behavior scholar and one of the promoters of evidence-based management. As in the rest of science in this period, there were fewer women leaders than men.

The author writes as a believer and her passion is captivating. Readers of the book are even encouraged to join the evidence revolution. And who can argue against better testing? After reading all of Pearson’s examples, it may seem strange to criticize the work of the heroes of this story. But it’s easy to lionize and boo defenders of the old ways when the reality is more complicated.

Not all medicine practiced before the era of RCTs and meta-analyses was a failure. Examples of such “eminence-based medicine” include defibrillation and insulin, which had demonstrable effects but were not rigorously tested. Pearson recognizes the benefits of penicillin, which has never been tested in an RCT.

It is not so easy in practice.