The paper presents a study aimed to validate the ability of the presently available models to predict the Cotton-Mouton effect. The Faraday rotation and the Cotton-Mouton phase shift angle can be calculated by means of the rigorous numerical solution of Stokes equations. Numerical and approximated solutions are presented and compared with experimental data. A detailed comparison is done with the complete time traces of measurements, inside a limited dataset representative of JET regimes. A statistical analysis is then carried out on a dataset including data from 300 discharged. In general the Cotton-Mouton measurements are in agreement with the numerical model, and the line integral of plasma density deduced by the Cotton-Mouton measurements is in agreement (well inside the experimental error, which is close to two fringes for the polarimetry measurements, 1 fringe = 1.14.1019 m-2) with that measured by interferometer and LIDAR Thomson scattering.