  The number-of-constituent-quark (NCQ) scaling behavior of the elliptic flow
of identified particles produced in A+A collisions is studied quantitatively
using an empirical function that fits the experimental $v_2$ data available
from the RHIC and LHC. The most common approach for NCQ scaling involves (1)
doing a scaling of the experimental $v_2$ data of an identified particle with
its NCQ, (2) doing the same to its transverse momentum or energy, then (3)
combining all the scaled data and identifying the NCQ behavior by intuitively
looking (since the measured experimental data are discrete). We define two
variables $(d_1, d_2)$ to describe NCQ scaling quantitatively and
simultaneously, and identify the approximate region where the NCQ scaling
holds. This approach could be applied to study NCQ or other scaling phenomena
in future experiments.
