Many reasons can explain why a paper is not listed within the ResearchScorecard database, mostly having to do with the source of the scientific literature used here, namely PubMed.

1. The institutional address provided by PubMed refers to where the work was performed. However, for a given paper PubMed cannot list multiple affiliations in cases where authors belong to different institutions. Therefore, ResearchScorecard can miss a paper for an author who is not associated with the institution listed by PubMed. ResearcherScorecard uses techniques to minimize this problem, but omissions will persist.

2. PubMed indexes papers several months after they have been published. Because ResearchScorecard relies on this indexing, the paper may be missing from its database.

3. ResearchScore does not access PubMed dynamically. If the paper appeared in PubMed after ResearchScorecard analyzed it, it will not be visible to our system until the next round of analysis.