Referring domains
Frequently Asked Questions
How many referring domains link to ncbi.nlm.nih.gov?
This page lists all unique domains that contain at least one backlink pointing to ncbi.nlm.nih.gov. Each referring domain is counted once regardless of how many individual links it contains. The count of referring domains is a stronger indicator of backlink profile strength than raw backlink count, because multiple links from the same domain carry diminishing returns.
What is the difference between backlinks and referring domains?
Backlinks are individual hyperlinks from other websites, while referring domains represent the unique websites those links come from. For example, if example.com links to your site from 5 different pages, that counts as 5 backlinks but only 1 referring domain. Search engines value diversity of referring domains more than sheer link volume, so 100 links from 100 different domains is generally more valuable than 100 links from a single domain.
Which referring domains have the highest authority?
The referring domains table for ncbi.nlm.nih.gov is sorted by Domain Rating (DR) by default, showing the most authoritative linking domains first. DR is scored from 0 to 100 based on each domain's own backlink profile. Links from high-DR domains pass more authority and have a greater impact on search rankings than links from low-DR domains.
How is referring domain quality measured?
Referring domain quality is measured using Domain Rating (DR), a score from 0 to 100 that reflects the strength of a domain's backlink profile. DR is calculated using a blend of two signals: the logarithmic count of effective referring domains (quantity) and PageRank percentile (quality). The result is calibrated against industry-standard benchmarks. A higher DR means the referring domain itself has strong backlinks, making its outbound links more valuable.