Patent–Paper Citation Linkage (NPL)

Non-patent literature, or NPL, refers to the references on a patent that point to sources other than patents, most importantly scientific journal articles but also conference papers, books, and standards. NPL matters because a reference from a patent to a scientific paper is a traceable link from technology to science. While patent-to-patent citations capture technological lineage, NPL references capture the scientific underpinnings of an invention. Narin and colleagues built the science-linkage indicator on exactly these references, using them to measure how strongly inventions draw on the published research base.

Ordinary patent citation analysis studies patent-to-patent citations to trace technological influence, value, and lineage among inventions. Patent–paper citation linkage instead focuses on the non-patent references that connect patents to the scientific literature, measuring science-technology coupling rather than technology-to-technology relationships. The two are complementary: patent citation analysis answers how technologies build on one another, while science linkage answers how technology builds on science. This NPL/science-linkage angle is what distinguishes the present method from patent-to-patent citation analysis and from general patent analysis.

No, and this is an important caveat. A patent-to-paper citation indicates a documented relationship between the invention and the cited research, but it does not by itself prove that the science directly enabled the invention; citations can be added by examiners, included for completeness, or reflect background context. Narin and colleagues treated linkage as an aggregate indicator that is meaningful in large numbers rather than as proof of use in any single case. Later work by Meyer and others examined precisely how reliably these citations signal genuine knowledge flows, urging cautious interpretation at the individual-patent level.