How psychological disorders are classified:
They're classified by symptom.
http://www.cliffsnotes.com/WileyCDA/CliffsReviewTopic/Classifying-Psychological-Disorders.topicArticleId-25438,articleId-25396.html
http://www.cliffsnotes.com/WileyCDA/CliffsReviewTopic/Classifying-Psychological-Disorders.topicArticleId-25438,articleId-25396.html