Study of the origins, philosophy and history of the criteria used to assess research activities in Spain by the CNEAI. The assessment criteria and quality evidence of publications is discussed. Results are presented on the temporal development of the criteria used, grouped by publication type (articles and books) and fields of knowledge. Between 1989-1996, assessment was based on the definition and goals set by the Spanish scientific framework and on general criteria. Between 1996-2004, the formulation of indicators began to be almost exclusively based on Journal Citation Reports (JCR). Success rates up to 2004 indicate that the evaluation criteria and publishing behaviour matched the "hard sciences", but not the Social Sciences and Economics. In 2005, the criteria used were further developed and reoriented with an eye to softening the preceding JCR-centrism by taking into consideration other databases and defining the quality criteria to be met by journals, books and conferences not included in JCR. Correspondingly, the success rates for 2007 indicate a dramatic recovery in Economics. In the last 4 years, Humanities and Social Sciences have consolidated the further opening of the criteria used with the addition of new benchmarks and the full integration of books.