What is Co-Citation?
Co-citation is the frequency at which two sites are jointly mentioned or quoted by other sites or sources. It typically indicates that the co-cited sites are related and relevant to themselves, even if they do not directly link to each other.
For example, if you publish a blog post containing backlinks pointing to Sites A and B, search engines may recognize that these two sites are related. This can, in turn, establish them as an authority and improve their visibility and rankings on search results pages.
Co-citation helps determine the relationship between two sites. The more two sites are co-cited, the more closely related they are considered. Co-citation also indicates that the co-cited documents are an authority in that topic, industry, or niche.
Examples of Co-Citation
Let us imagine a situation where two URLs, A and B, contain links pointing to URL C. However, URLs A and B do not directly link to one another, so they are considered co-cited.
You can think of the relationship between URLs A and B as a virtual backlink connecting both sites together. The backlink is not physically there, but Google may treat both sites as if it is there.
The more sites URLs A and B link to, the more co-cited they become. For example, if URLs A and B also link to URLs D, E, and F, they are more co-cited and relevant to one another.
Importance of Co-Citation
Co-citation functions as a form of virtual backlink connecting two sites together. So, it provides both sites with certain benefits, as if there is an actual link connecting them together. For instance, it informs Google that both co-cited sites are relevant to one another.
Co-citation also helps the co-cited sites establish their authority, rankings, and visibility on Google results pages. This further positions the sites as an authority and makes them more visible to other sites that may link to them.
Co-citations may also help Google identify spammy sites. Specifically, when multiple spammy or low-quality sites repeatedly mention or link to a site, Google may begin to consider the sites as being part of a link farm of private blog network (PBN).
Relevance of Co-Citation to SEO
Co-citations became relevant to SEO after Google released the first Penguin update on April 24, 2012. Penguin targeted sites that engaged in manipulative link building schemes. This made link building difficult as multiple black hat link building techniques became less effective than they used to be.
It is speculated that Penguin uses co-citation to understand the relationship between the site providing the link and the one receiving it.
Before Penguin, Google only focused on the URL receiving the link. This meant the keywords used in an anchor text influenced how a page ranked. As a result, it was common for bloggers to stuff keywords into the anchor texts to improve their rankings.
However, with Penguin, Google now focuses on the content of the URL from which the URL originates. It also considers the context in which the text containing the anchor text is used. This means that Google better understands the relationship between the published content at both URLs.
Penguin and co-citation led to the rise of what bloggers call linkless optimization. This means a site can rank for certain keywords even when they are not specifically optimized for it.
In all, co-citation marked a change in SEO. Its arrival ended the over-optimization of anchor texts. It also somewhat reduced the impact of direct link building since a link does not physically need to exist before Google determines that two pieces of content are relevant to one another.
That said, this does not mean that link building is dead. You will still need to build links. Remember that co-citation depends on links, not just directly.