Bibliometrics are tools used to give a quantitative measure of the impact of a piece of research, or a researcher's body of work, or a research institute's research output, etc. Often these tools are broken up into "Metrics" and "Altmetrics".
The generic term metrics or traditional metrics are used in bibliometric reports or bibliometric research to refer to measures like citation count, h-index, journal impact factor, etc. These are measures of how many researchers could have seen and/or used the research in question. Traditional metrics usually require a wait of a couple of years before they are worth calculating, because it takes time for other researchers to do, write up, submit, and publish articles that cite the article in question.
Altmetrics, alt-metrics or alternative metrics are used to describe measures like number of shares on social media, number of mentions in news stories, how many downloads, etc. These are measures of interest, awareness and possible impact in the wider world. Altmetrics are usually very fast, involving a flood of attention when the article in question is first published, and then slowing down as discussion moves on to newer topics.
Metrics, usually traditional, are often used in academic settings for hiring, promotion, tenure etc. You may also be asked for metrics (again, usually traditional) for research grant applications and in other circumstances where someone is deciding between multiple researchers.
Both traditional and alternative metrics have their weaknesses as tools for measuring the importance and impact of a research study, a researcher or a research institute.
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