The Four-Item Mentalising Index (FIMI) Is a Valid, Reliable, and Practical Way to Assess Mentalising: Reply to Murphy et al. (2022)

Murphy et al. (2022) raised concerns regarding the validity of the Four-Item Mentalising Index (FIMI). We wholeheartedly agree with Murphy et al. that there are problems in the social cognition literature hampering research. However, we maintain the FIMI is conceptually grounded in empirical and theoretical research, and that concerns regarding its construct validity are overstated. Drawing on recent research, we also discuss issues concerning the interpretation of discriminant validity analyses and discuss approaches to improve objectivity in future research. Overall, we argue that the FIMI is a conceptually and psychometrically sound measure, which has utility in future social cognition research and clinical practice. Public Significance Statement We discuss a recent critique of a new mentalising measure, the Four-Item Mentalising Index (FIMI). We agree there are issues within the social cognition literature, but argue that the criticisms put forth about the FIMI are overstated. Using recent literature to support our arguments, we maintain that the FIMI is a valid, reliable, and valuable new tool for measuring mentalising.