The article by Fleming and Lau reviews methods for quantifying metacognition, focusing on measures that assess the correspondence between trial-by-trial accuracy and confidence. They distinguish between metacognitive sensitivity (ability to distinguish correct from incorrect judgments) and metacognitive bias (difference in subjective confidence despite constant task performance). The authors discuss various measures, including correlation coefficients (phi and gamma), type 2 $d'$, and receiver operating characteristic (ROC) analysis, emphasizing the importance of bias-free measures. They introduce the meta-$d'$ measure, which is based on an ideal observer model and is robust to changes in bias. The article also explores the implications of these measures for understanding metacognitive efficiency and their potential applications in comparing metacognitive abilities across different domains and species. Additionally, it discusses the relationship between metacognition and conscious awareness, cautioning against equating metacognitive sensitivity directly with awareness.The article by Fleming and Lau reviews methods for quantifying metacognition, focusing on measures that assess the correspondence between trial-by-trial accuracy and confidence. They distinguish between metacognitive sensitivity (ability to distinguish correct from incorrect judgments) and metacognitive bias (difference in subjective confidence despite constant task performance). The authors discuss various measures, including correlation coefficients (phi and gamma), type 2 $d'$, and receiver operating characteristic (ROC) analysis, emphasizing the importance of bias-free measures. They introduce the meta-$d'$ measure, which is based on an ideal observer model and is robust to changes in bias. The article also explores the implications of these measures for understanding metacognitive efficiency and their potential applications in comparing metacognitive abilities across different domains and species. Additionally, it discusses the relationship between metacognition and conscious awareness, cautioning against equating metacognitive sensitivity directly with awareness.