Final answer:
Psychological disorders in the U.S. are diagnosed using the DSM, which is published by the American Psychiatric Association, not the American Psychological Association as mentioned in the question.
Step-by-step explanation:
In the United States, psychological disorders are primarily diagnosed and classified according to the guidelines established by the American Psychiatric Association (APA) through the publication of the Diagnostic and Statistical Manual of Mental Disorders, commonly known as the DSM. The most recent edition at the time of this response being the DSM-5. It is crucial to note that while the American Psychological Association (also abbreviated as APA) contributes to the discipline of psychology in various ways, it is the American Psychiatric Association that actually publishes the DSM, which is used for diagnosis.
The evolution of the DSM has involved considerable discussion regarding how to best classify and approach the treatment of psychological disorders, including personality disorders. The final publication of the DSM retains the original ten categories of personality disorders, with an additional alternative model to aid in diagnosis and classification. This ongoing evolution reflects both the complexity of mental health conditions and the collaboration among professionals in the field.
Therefore, the correct answer to the student's question is a) American Psychological Association (APA), as this organization is responsible for the development and publication of the DSM used for diagnosing psychological disorders.