The citation impact outside references - formal versus informal citations

In this study the amount of informal citations (i.e. those mentioning only author names or their initials instead of the complete references) in comparison to the formal (full reference based) citations is analyzed using some pioneers of chemistry and physics as examples. The data reveal that the formal citations often measure only a small fraction of the overall impact of seminal publications. Furthermore, informal citations are mainly given instead of (and not in addition to) formal citations. As a major consequence, the overall impact of pioneering articles and researchers cannot be entirely determined by merely counting the full reference based citations.