In our lab, 299 real judges from seven major jurisdictions (Argentina, Brazil, China, France, Germany, India, and USA) spend up to fifty-five minutes to judge an international criminal appeals case and determine the appropriate prison sentence. The lab computer (i) logs their use of the documents (briefs, statement of facts, trial judgment, statute, precedent) and (ii) randomly assigns each judge (a) a horizontal precedent disfavoring, favoring, or strongly favoring defendant, (b) a sympathetic or an unsympathetic defendant, and (c) a short, medium, or long sentence anchor. Document use and written reasons differ between countries but not between common and civil law. Precedent effect is barely detectable and estimated to be less, and bounded to be not much greater than, that of legally irrelevant defendant attributes and sentence anchors. © 2021 The Author(s) 2021. Published by Oxford University Press on behalf of The John M. Olin Center for Law, Economics and Business at Harvard Law School.