Inference with legal evidence: common sense is necessary, but not sufficient

Recent cases have highlighted the issue of faulty probabilistic reasoning by expert witnesses in courts of law. While concern about potential miscarriages of justice is clearly well-placed, the consequences of such faulty reasoning do not seem to be fully appreciated. These are often counter-intuitive, as we show with two examples: the Interrogator's Fallacy and the Prosecutor's Fallacy. Both demonstrate the danger of relying solely on 'common sense' when drawing inferences from legal evidence.