Effect structure in physics and hints to economics equation of state

We point out that, there is effect structure in physical laws which is noticed from both phenomenological and postulate points of view. Here we consider effect structure in equations of state (EoS). Effect of one variable to the other variables are expressed as a diagram. Formal criteria to judge a status of EoS of an empirical relation is proposed here for classifying the EoS into classes. The framework shades light on testing of existence of an EoS in economics system. Demand-side EoS in perfect-competitive market is proposed employing hints given by the criteria. The demand-side EoS turns to be new class of EoS.