To protect people from Electromagnetic Fields (EMF), ICNIRP has defined limits [1]. The Basic Restrictions (BR) set the maximum values of Specific Absorption Rate (SAR). Since BR are complex to assess ICNIRP has also derived the reference levels (RL) from BR. These RL were established to guaranty the compliance to BR. Several studies with human model (phantoms) show that even below the RL, the WBSAR (Whole Body averaged SAR) may exceed the BR due to the variability of human morphology [2]. The number of phantoms is very limited. Hence, t e characterization of the WBSAR for a given using usual methods such as Monte Carlo is not possible. To bridge this lack of phantoms a model for the WBSAR as a function of morphology is suitable. However, this model requires knowledge on internal morphology (proportion of fat, muscle...) and external ones (mainly height and weight) [5]. Due to the absence of statistical data concerning the internal morphology, the statistical distribution of the WBSAR is difficult to obtain. In this paper, the internal morphology is released by considering one equivalent tissue for the whole body. The stochastic collocation is used to characterize the distribution of the WBSAR for a given population. The study is conducted in the case of a plane wave operating at 2.1 GHz, vertically polarized and frontally oriented on phantoms. The incident power is equal to 1W/m².