[en] The results of the IAEA ''Coordinated Research Programme on Irradiation Embrittlement of Pressure Vessel Steels'' were examined again to analyse the reasons behind the reported large scattering and discrepancies in the effect of irradiation on the ductile-brittle transition temperature (DBTT). It is concluded that using specimens from different locations throughout the HSST steel plate thickness was the main reason behind the scattering in these results. Specimens from different locations had different microstructures and different initial mechanical properties which led to different irradiation sensitivities. The analysis showed that the specimens used can be considered to consist of two sets different in microstructure, mechanical properties and irradiation sensitivity. Set 1 composed of specimens taken from positions between T/4 and T/2 throughout the plate thickness while set 2 composed of specimens taken from positions between the surface and T/4. In this way the scattering became very small and even negligable and the discrepancies were explained. (orig.)