• What terminology, definitions, and frameworks for the classification of voice disorders are described in the published literature?  
• What clinical criteria exist to guide clinicians in the classification of voice disorders? 
• Do the existing classification systems satisfy methodological guidelines for the development of classification systems?

This review will consider participants (adults and children) that have been diagnosed with a voice disorder using any diagnostic criteria or framework.  

This review will consider a broad range of studies that report on patients with a voice disorder and include: 1) the development or description of a voice disorder classification framework and / or classification criteria (i.e. groups of conditions); 2) a description of defined criteria used to describe one or more voice disorder classification group(s) / framework.

Studies considered for inclusion will: 1) provide enough descriptive detail of the structure of the classification system to allow for a summary description; 2) use well defined methodological approaches to determine a set of criteria.  (e.g. a consensus approach based on expert opinion; statistical modeling; systematic literature reviews; methods considering multiple diagnostic tests).

The review will consider geographical and clinical contexts (specifically the treating professions) where the classification of voice disorders has been employed.