You Understand, So I Understand: How a “Community of Knowledge” Shapes Trust and Credibility in Expert Testimony Evidence

Sloman and Rabb found support for the existence of the community of knowledge (CK) effect, which occurs when individuals are more likely to report understanding and being able to explain even fake scientific information when told that an expert understands the information. To date, no studies have been conducted that attempted to replicate original findings, let alone test the presence of the CK effect in realistic, legal scenarios. Therefore, Study One replicated original CK effect studies in a jury-eligible M-Turk sample (<i>N</i> = 291) using both Sloman and Rabb’s experimental stimuli as well as new stimuli. Study Two then tested the presence of the CK effect using scientific testimony in a mock court hearing from a forensic evaluator (<i>N</i> = 396). Not only did the CK effect improve laypeople’s perceptions of the scientific information in court, but it also improved their perceptions of the expert witness’s credibility, increased the weight assigned to the scientific information, and increased the weight assigned to the expert testimony. This effect was mediated by participants’ perceived similarity to the expert, supporting the theory behind the CK effect. These studies have important implications for the use of scientific information in court, which are discussed.