Altmetrics are “alternative metrics” to measure the influence and reach of scholarly output on the Web through peer-review counts, influential news sites and blog posts, citation manager bookmarks such as Mendeley, Wikipedia citations, and social media mentions on sites such as Twitter and Facebook.
Altmetrics go beyond the traditional citation metrics to take into consideration how scholarly output such as journal articles and research datasets are being cited and shared by others on the Web in order to measure influence. They are meant to complement traditional metrics, not replace them.
Altmetrics counts (and scores) are updated much more quickly than traditional citation counts so are especially helpful with “hot topics” getting mainstream attention where citation counts can lag by months and even years.
Altmetrics measure the influence an article has by analyzing citations and sharing activity. The higher the altmetrics score, the wider the dissemination of the work.
Altmetrics are basically counts of mentions and links to scholarly journals and datasets from reputable news sites (and aggregators) and blogs, peer-reviewed sites, reference managers, and major social media sites.
The company Altmetric uses a weighted score with a news article counting 8 points, a blog post counts 5, a Wikipedia link is 3, and a Twitter post counts as 1 point. Sources counting less than 1 point include Facebook and YouTube at 0.25 point and LinkedIn at 0.5.
Other altmetrics sources use a simple count of "mentions" with no weighting applied. Score from different sources aren't directly comparable, but a higher score generally means a more influential scholarly work.