Satellite Based Augmentation systems (SBAS) provide to Global Navigation Satellite Systems (GNSS) users with an extra set of information, in order to enhance accuracy and integrity levels of GNSS stand alone positioning. In this context, different test methods to analyze the ionospheric corrections performance are presented. The first set of tests involves two of the ionospheric calculations that are applied daily to the Global Ionospheric Maps (GIM), computed by the IGS Associate Analysis Centers: a TEC TOPEX comparison test and the STEC variations test. The second family of tests provides two very accurate analyses based on large-baselines ambiguity resolution techniques giving comparisons for absolute STEC and double differenced STEC determinations. Those four analyses have been applied using EGNOS System Test Bed (ESTB) data showing some satellite dependent biases.