Final answer:
The DSM-III introduced a multiaxial system, removed etiological assumptions for a more descriptive approach, and implemented standardized diagnostic criteria, marking a key shift in the classification of mental disorders.
Step-by-step explanation:
The DSM-III, introduced by the American Psychiatric Association in 1980, marked a significant shift in the classification of mental disorders. One of the fundamental assumptions was the implementation of a multiaxial system that allowed for a more comprehensive assessment of the individual. This system included five axes which considered not only the clinical disorders but also personality disorders, physical conditions, severity of psychosocial stressors, and the level of functioning.
Another assumption was the removal of the etiological assumptions that were prevalent in earlier versions. The DSM-III aimed to be more empirically based and atheoretical, focusing on clusters of symptoms to define disorders, which is considered a descriptive approach. This change aimed to increase the reliability of diagnoses across different clinicians and settings.
Additionally, the introduction of the DSM-III placed a greater emphasis on standardized diagnostic criteria. Each mental disorder was defined by specific criteria that had to be met for a diagnosis to be assigned. This was a key development in creating a more objective and reliable way to diagnose mental health conditions.