  The order parameter for a continuous transition shows diverging fluctuation
near the critical point. Here we show, through numerical simulations and
scaling arguments, that the inequality (or variability) between the values of
an order parameter, measured near a critical point, is independent of the
system size. Quantification of such variability through Gini index ($g$),
therefore, leads to a scaling form $g=G\left[|F-F_c|N^{1/d\nu}\right]$, where
$F$ denotes the driving parameter for the transition (e.g., temperature $T$ for
ferromagnetic to paramagnetic transition transition, or lattice occupation
probability $p$), $N$ is the system size, $d$ is the spatial dimension and
$\nu$ is the correlation length exponent. We demonstrate the scaling for the
Ising model in two and three dimensions, site percolation on square lattice and
the fiber bundle model of fracture.
