Your text describes a study of the reliability of diagnoses for several types of mental disorders which concludes that

The answer to this question is the diagnostic categories of the DSM are not always used reliably by clinicians.

In order to use DSM correctly, clinicians had to pay attentions to several acts that displayed by the patient at the same time. A lot of clinicians often mistaking a certain display of behavior into something else that will affect the end result of the diagnosis.