Source Publication (e.g., journal title)
For many decades it was the only major commercial system to use citation measures. Since 2004, Elsevier's Scopus and Google Scholar have also provided various citation measures, including impact factor and number of cited references. Authors may cite something they disagree with, rather than believe is of high quality; an author who publishes a lot may accumulate the same number of citations as an author with one seminal and highly cited paper. Because citing patterns vary by subject discipline, journal impact factors should not be used across disciplines nor to measure quality of individual authors.
Tenopir, Carol. “Measuring Impact and Quality,” Library Journal 132 (September 1, 2007).