A citation to an earlier work is an indication of use and usually an endorsement. Occasionally citations are made because earlier research is being disputed or disproved. Most publisher and other fulltext databases that include the cited reference lists and/or full text will link to citing articles within that database. Examples include JSTOR, Wiley Interscience, ScienceDirect, Highwire, Annual Reviews, PMC, etc. While this is useful for finding related information, the scope is limited. Citation metrics have different implications for articles, books, data, and software; for more information, see Virginia Tech's Guide and University of Michigan's Guide.