ders. Finding the right balance is critical. Speculative results do not belong in an official
nosology, but at the same time, DSM must evolve in the context of other clinical research ini-
tiatives in the field. One important aspect of this transition derives from the broad recognition
that a too-rigid categorical system does not capt ure clinical experience or important scientific
observations. The results of nu merous studies of comorbidity and disease transmission in fam-
ilies, including twin studies and molecular genetic studies, make strong arguments for what
many astute clinicians have long observed: the boundaries between many disorder “catego-
ries” are more fluid over the li fe course than DSM-IV recognized, and many symptoms as-
signed to a single disorder may occur, at vary ing levels of severity, in many other disorders.
These findings mean that DSM, like other medi cal disease classifications, should accommo-
date ways to introduce dimens ional approaches to mental di sorders, including dimensions
that cut across current categories. Such an appr oach should permit a more accurate description
of patient presentations and increase the validity of a diagnosis (i.e., the degree to which diag-
nostic criteria reflect the comprehensive mani festation of an underlying psychopathological
disorder). DSM-5 is designed to better fill the need of clinicians, patients, families, and re-
searchers for a clear and concise description of ea ch mental disorder organized by explicit di-
agnostic criteria, supplemented, when approp riate, by dimensional measures that cross
diagnostic boundaries, and a brie f digest of information about th e diagnosis, risk factors, as-
sociated features, research advances, and various expressions  of the disorder. 
Clinical training and experience are needed to use DSM for determining a diagnosis. The
diagnostic criteria identify symptoms, behavior s, cognitive functions, personality traits, phys-