Methodological considerations on the use of the normalized impact in the Severo Ochoa and Mar\'ia de Maetzu programmes

In 2011, the programme for Severo Ochoa Centers of Excellence and Mar\'ia de Maeztu Units of Excellence was launched for the first time. Since this programme has become one of the axes of the Spanish scientific policy. 186 million euros have been distributed and 26 centers and 16 units have been accredited. One of the most relevant criteria for submission is the need for guarantor researchers to have a Normalized Impact of 1.5. In this work, we critically analyze the origin of this bibliometric indicator rooted in the 1980s, the different variants that have been proposed and the limitations its use in this programme have. Finally, we offer a series of practical recommendations for a more accurate use of normalized impact indicators for evaluative purposes.