What is the best way to present likelihood ratios? A review of past research and recommendations for future research

As a first step in addressing the research question “What is the best way for forensic practitioners to present likelihood ratios so as to maximize their understandability for legal-decision makers?”, this paper reviews existing empirical literature on the comprehension of likelihood ratios by laypersons. The existing literature tends to research understanding of expressions of strength of evidence in general, rather than focusing specifically on likelihood ratios. We review the literature with respect to the CASOC indicators of comprehension (particularly sensitivity, orthodoxy, and coherence), and compare different formats that have been used to express likelihood ratios: numerical likelihood-ratios values, numerical random-match probabilities, and verbal strength-of-support statements (none of the studies that we reviewed tested comprehension of verbal likelihood ratios). We also critically review the studies with respect to methodology, and consider additional factors that could potentially assist with communication of the meaning of likelihood ratios. We conclude that the existing literature does not answer our research question, but, based on our review, we provide recommendations for the methodology of future research aimed at addressing our research question.