Functional balance is defined as follows
$$%
P^{-1}\sum_{p}\left(1 - \left|0.5 - N^{-1}\sum_n a_{np}\right|\right)
$$
Where A
is the matrix of annotations.
With values ranging between 0 and 1, one been perfect balance, this is, equal
number of zeros and ones in the annotations. In the case of multiple functions,
as noted in the formula, the balance is the average across functions.