Current developments and challenges in the assessment of negative symptoms.

Reliable and valid assessment of negative symptoms is crucial to further develop etiological models and improve treatments. Our understanding of the concept of negative symptoms has undergone significant advances since the introduction of quantitative assessments of negative symptoms in the 1980s. These include the conceptualization of cognitive dysfunction as separate from negative symptoms and the distinction of two main negative symptom factors (avolition and diminished expression). In this review we provide an overview of existing negative symptom scales, focusing on both observer-rated and self-rated measurement of negative symptoms. We also distinguish between measures that assess negative symptoms as part of a broader assessment of schizophrenia symptoms, those specifically developed for negative symptoms and those that assess specific domains of negative symptoms within and beyond the context of psychotic disorders. We critically discuss strengths and limitations of these measures in the light of some existing challenges, i.e. observed and subjective symptom experiences, the challenge of distinguishing between primary and secondary negative symptoms, and the overlap between negative symptoms and related factors (e.g. personality traits and premorbid functioning). This review is aimed to inform the ongoing development of negative symptom scales.