The Monotony Criterion for A Finite Size Scaling Analysis of Phase   Transitions
  We propose a new criterion to analyse the order of phase transitions within a finite size scaling analysis. It refers to response functions like order parameter susceptibilities and the specific heat and states different monotony behaviour in volume for first and second order transitions close to the transition point. The criterion applies to analytical and numerical studies of phase diagrams including tricritical behaviour. 
H. Meyer-Ortmanns and T. Reisz