A s noted in the Introduction and Chapter 2 of this volume, symptom-based rating scales, structured interviews, and psychological assessment instruments are different methods of inquiry, often undertaken for different diagnostic purposes. As such, it is important not to lose sight of the epistemological differences between rating scales and psychological assessment methods. In addition to identifying symptoms, psychological assessment methods are best suited to measuring underlying psychological functions or capacities, such as perception and thought processes, as well as describing the organization and dynamics of an individual personality. Rating scales, on the other hand, are typically focused on the presence or absence of a specific diagnostic entity and its manifest symptoms.Rating scales are used to assess the presence of symptoms, levels of severity, dimensions of symptoms (e.g., intensity, duration, disruptiveness, ability to resist) and response to treatment in individuals with a broad range of psychopathology. Their use in assessing psychotic symptomatology is widespread in scientific studies and clinical settings (Kleiger & Khadivi, 2015;Waters & Stephane, 2015). Several resources for learning about available rating scales include the previous references and Johnson (2010). Kleiger and Khadivi (2015) and Johnson organized their appendix of scales categorically. Waters and Stephane (2015) and Johnson provided contact information about where scales may be obtained. Review of psychometric properties and factor structures