Positive findings are around twice as likely to be published as negative findings. This is a cancer at the core of evidence-based medicine.

Goldacre is pointing to publication bias: studies with “positive” results (showing an effect) are disproportionately published, while null or negative results often remain unseen. In evidence-based medicine, this skews the apparent balance of evidence, inflating perceived benefits and obscuring harms, because clinicians and guideline writers typically rely on the published literature. Calling it “a cancer at the core” emphasizes that the problem is systemic rather than occasional misconduct: even well-run trials can collectively mislead if the record is selectively visible. The quote also implies a moral and practical imperative for trial registration, full reporting, and open data so medical decisions reflect the totality of evidence, not just the most publishable outcomes.