The variations which happen in the troposphere layers throughout the time in relation to the median condition of the signal cause various phenomena that change the received signal level at digital radio relay systems randomly. The random changes are named fading. Fading is normally classified as fast or slow. The former is normally associated with the atmospheric multipath propagation and is strongly dependent on frequency; therefore, this is named selective fading and it is normally the cause of performance degradation in high capacity digital radio relays. The existing models for statistics of multipath fading are semi - empirical and based on experimental data extracts from regions the climate of which is temperate; and this gives a rough estimate with respect to the tropical and equatorial zones. This work presents an evaluation of existing methods of performance prediction for high capacity digital radio relay systems using real performance data obtained from measures of a high capacity digital radio link in operation in the tropical region.