  For a system near a second order phase transition, the probability
distribution for the order parameter can be given a finite size scaling form.
This fact is used to compare the finite temperature phase transition for the
Wilson lines in d=3+1 SU(2) lattice gauge theory with the phase transition in
d=3 phi^4 field theory. I exhibit the finite size scaled probability
distributions in the form of a function of two variables (the reduced
`temperature' and the magnetization) for both models. The two surfaces look
identical, and an analysis of the errors also suggests that they are the same.
This strengthens the idea that the SU(2) effective line theory is in the Ising
universality class. I argue for the wider application of the method used here.
