Objective
In the DSM-III and the DSM-IV, bipolar disorder (BD) is classified as a mood disorder and diagnosis requires presence of a mood change, i.e., euphoria or irritability. In contrast, DSM-5 states that there must be some increase in energy or motor activity in addition to the mood change. Our aim was to identify which types of symptoms (i.e., mood or energy/activity-related symptoms) are the most informative in a manic episode.

Methods
Symptoms of manic episodes in 106 outpatients with BD were assessed in a naturalistic study using the Young Mania Rating Scale (YMRS) between November 2002 and November 2015. The scale items were divided into three groups according to clinical criteria: mood, energy/activity, and other. For comparisons between groups, the Samejima graded response model from Item Response Theory (IRT) and the Test Information Function (TIF) were computed. Chi-square tests were used to verify the association between the groups of symptoms by comparing the area under the curve of the TIF results.

Results
The information accounted for by energy/activity represents 77% of the proportion of the total TIF; about 23% is related to mood and other groups of symptoms. These proportions are statistically different (χ2[1] = 30.42, p < 0.001)

Conclusion
On average, changes in energy/activity tend to be more informative than mood changes during the manic phases of BD.