M usicians are typically identified in research papers by some single item measure (SIM) that focuses on just one component of musicality, such as expertise. Recently, musical sophistication has emerged as a more comprehensive approach by incorporating various components using multiple question items. However, the practice of SIM continues. The aim of this paper was to investigate which SIM in musical sophistication indexes best estimates musical sophistication. The Ollen Musical Sophistication Index (OMSI) and the Goldsmiths Musical Sophistication Index (Gold-MSI) were analyzed. The OMSI musician rank item (“ Which title best describes you? ”) was observed to be the best SIM for predicting OMSI and Gold-MSI scores. Analysis of the OMSI item indicated three parsimonious musical identity categories (MIC); namely, no musical identity (NMI), musical identity (MI), and strong musical identity (SMI). Further analyses of MIC against common SIMs used in literature showed characteristic profiles. For example, MIC membership according to years of private lessons are: NMI is < 6 years; MI is 6–10 years; and SMI is > 10 years. The finding of the study is that the SIM of musician rank should be used because of its face validity, correlation with musical sophistication, and plausible demarcation into the three MIC levels.