SJR and SNIP
SCImago Journal Rank)
SJR is weighted by the prestige of a journal Subject field, quality, and reputation of the journal have a direct effect on the value of a citation.
SJRassigns relative scores to all of the sources in a citation network. Its methodology is inspired by the Google PageRank algorithm, in that not all citations are equal. A source transfers its own 'prestige', or status, to another source through the act of citing it. A citation from a source with a relatively high SJR is worth more than a citation from a source with a lower SJR.
A source's prestige for a particular year is shared equally over all the citations it makes in that year; this is important because it corrects for the fact that typical citation counts vary widely between subject fields. The SJR of a source in a field with a high likelihood of citing is shared over a lot of citations, so each citation is worth relatively little. The SJR of a source in a field with a low likelihood of citing is shared over few citations, so each citation is worth relatively much. The result is to even out the differences in citation practice between subject fields and facilitate direct comparisons of sources.
SJR emphasizes those sources that are used by prestigious titles.SJR allows the user to rank their own customized set of sources, regardless of their subject fields.
Source Normalized Impact per Paper
SNIP measures a source’s contextual citation impact by weighting citations based on the total number of citations in a subject field. It helps you make a direct comparison of sources in different subject fields.
SNIP takes into account characteristics of the source's subject field, which is the set of documents citing that source. SNIP especially considers
- the frequency at which authors cite other papers in their reference lists
- the speed at which citation impact matures
- the extent to which the database used in the assessment covers the field’s literature
SNIP is the ratio of a source's average citation count per paper and the citation potential of its subject field.
The citation potential of a source's subject field is the average number of references per document citing that source. It represents the likelihood of being cited for documents in a particular field. A source in a field with a high citation potential tends to have a high impact per paper.
Citation potential is important because it accounts for the fact that typical citation counts vary widely between research disciplines. For example, they tend to be higher in life sciences than in mathematics or social sciences. If papers in one subject field contain an average of 40 cited references while those in another contain an average of 10, then the former field has a citation potential that is 4 times higher than that of the latter.
Citation potential also varies between subject fields within a discipline. For instance, basic journals tend to show higher citation potentials than applied or clinical journals, and journals covering emerging topics tend to have higher citation potentials than periodicals in well established areas.