A comparison between numeric confidence ratings and verbal confidence statements

Is confidence most diagnostic of accuracy when expressed in numbers or when expressed in words? This question bears immense importance in many real-world contexts especially within the confines of eyewitness identification. In an eyewitness identification task, we compared the diagnostic value of numeric confidence across rating scales that varied in grain size (3-point vs. 6-point vs. 21-point vs. 101-point rating scales). We also compared the diagnostic value of numeric confidence to verbal confidence statements using several machine-learning algorithms. We found that fine-grain ratings are more diagnostic of identification accuracy than coarse-grain ratings, which suggests that the former provides a closer correspondence to memory strength than the latter. Moreover, we found that verbal confidence statements capture diagnostic information about the likely accuracy of an identification that numeric confidence ratings do not capture. This suggests that verbal confidence statements and numeric confidence ratings reflect partially independent, nonoverlapping sources of information. These results shed light on the processes that provide diagnostic value to confidence. From an applied standpoint, these results suggest that verbal confidence statements and numeric confidence ratings ought to be collected from eyewitnesses after an identification decision. Collecting both captures more diagnostic information than either can capture in isolation. (PsycInfo Database Record (c) 2025 APA, all rights reserved).