Introduction

Most patients likely assume that physicians offer medical procedures backed by solid, scientific evidence that demonstrates their superiority—or at least non-inferiority—to alternative approaches.1 Doing otherwise would waste healthcare resources urgently needed elsewhere in the system and also would jeopardise patient health and safety as well as undermine patients’ trust in medicine2 and care. In some instances, however, physicians’ healthcare practices appear to act against scientific evidence.3–5 For example, evidence from two large randomised controlled trials6 7 on ovarian cancer screening’s effectiveness showed that the screening has no mortality benefits—neither cancer-specific nor overall—in average-risk women but considerable harms, including false-positive surgeries in women without ovarian cancer. Consequently, the US Preventive Services Task Force and medical associations worldwide recommend against ovarian cancer screening.8 Nevertheless, a considerable number of US gynaecologists persist in recommending the screening to average-risk women.9 To understand why physicians continue using a practice called into question by scientific evidence, we investigated gynaecologists’ reasons for or against recommending ovarian cancer screening, their assumptions about why other gynaecologists recommend it, and the association between their knowledge of basic concepts of cancer screening statistics10 and recommendation behaviour.