  The thermodynamics of the O(N) model in 1+1 dimensions is studied applying
the CJT formalism and the auxiliary field method as well as fully
nonperturbative finite temperature lattice simulations. The numerical results
for the renormalized mass of the scalar particles, the pressure and the trace
anomaly are presented and compared with the results from lattice simulation of
the model. We find that when going to the two loop order we observe a good
correspondence between the CJT formalism and the lattice study.
