About Impact per Publication (IPP)
The IPP measures the ratio of citations in a year (Y) to scholarly papers published in the three previous years (Y-1, Y-2, Y-3) divided by the number of scholarly papers published in those same years (Y-1, Y-2, Y-3). The IPP metric is using a citation window of three years which is considered to be the optimal time period to accurately measure citations in most subject fields. Taking into account the same peer-reviewed scholarly papers only in both the numerator and denominator of the equation provides a fair impact measurement of the journal and diminishes the chance of manipulation.
The IPP is not normalized for the subject field and therefore gives a raw indication of the average number of citation a publication published in the journal will likely receive. When normalized for the citations in the subject field, the raw Impact per Publication becomes the Source Normalized Impact per Paper (SNIP). Note that in the context of the calculation of SNIP, the raw Impact per Publication is usually referred to as RIP. Like SNIP, the raw Impact per Publication metric was also developed by Leiden University's Centre for Science & Technology Studies (CWTS).
- Research Paper: "Measuring contextual citation impact of scientific journals"
This paper explores the methodology behind the raw Impact per Publication and the Source-Normalized Impact per Paper (SNIP).
- CWTS website
From this site, you can find raw impact per publication values and related in-depth information about journals.