• Even when the intention was to identify identical patient populations, DSM-IV and
ICD-10 diagnoses did not always agree.
Early in the course of the revisions, it be came apparent that a shared organizational
structure would help harmonize the classificatio ns. In fact, the use of a shared framework
helped to integrate the work of DSM and ICD work groups and to focus on scientific is-
sues. The DSM-5 organization and the proposed linear structure of the ICD-11 have been
endorsed by the leadership of the NIMH Resear ch Domain Criteria (RDoC) project as con-
sistent with the initial overa ll structure of that project.
Of course, principled disagreements on th e classification of psychopathology and on
specific criteria for certain disorders were expected given the current state of scientific
knowledge. However, most of  the salient differences betw een the DSM and the ICD classi-
fications do not reflect real sc ientific differences, but rather represent historical by-products
of independent committee processes. 
To the surprise of participants in both revi sion processes, large sections of the content
fell relatively easily into place, reflecting real strengths in some areas of th e scientific lit-
erature, such as epidem iology, analyses of comorbidity, twin studies, and certain other ge-
netically informed designs. When disparities emerged, they almost always reflected the
need to make a judgment about where to plac e a disorder in the face of incomplete—or,
more often, conflicting—d ata. Thus, for example, on the ba sis of patterns of symptoms, co-
morbidity, and shared risk factors, attentio n-deficit/hyperactivity disorder (ADHD) was
placed with neurodevelopmental  disorders, but the same data also supported strong ar-