  We introduce a parameter $W(\beta,L)= (\pi\,\langle |m| \rangle^2/\langle m^2
\rangle - 2)/(\pi-2)$ which like the kurtosis (Binder cumulant) is a
phenomenological coupling characteristic of the shape of the distribution
$p(m)$ of the order parameter $m$. To demonstrate the use of the parameter we
analyze extensive numerical data obtained from density of states measurements
on the canonical simple cubic spin-$1/2$ Ising ferromagnet, for sizes $L=4$ to
$L=256$. Using the $W$-parameter accurate estimates are obtained for the
critical inverse temperature $\beta_c = 0.2216541(2)$, and for the thermal
exponent $\nu = 0.6308(4)$. In this system at least, corrections to finite size
scaling are significantly weaker for the $W$-parameter than for the Binder
cumulant.
