Scientometrics is a branch of statistics concerned with the quantification of scientific activities. Traditionally, it focused on citation patterns (a subfield also known as bibliometrics), i.e. the number of citations a scholarly publication has garnered from a reference pool of peer-reviewed academic journals over a given period of time. An example of a widely used (and misused) bibliometric measure is the Journal Impact Factor. With the advent of electronic publishing, measures derived from usage patterns have also become popular and drive the development of article-level metrics.