Linking and non-linking root domains

[halloranc]

Hi,

Is there any affect on SEO based on the ratio of linking root domains to non-linking root domains and if so what is the affect?

Thanks

[customerparadigm.com]

Casey - Let me take a quick stab at your question.

I think that you are asking what affect a non-followed link vs. a followed link has on SEO rankings for a site?

If so, then the answer is that generally, nofollow links coming into your site don't help your SEO efforts. That said, the real answer is a little murky, and I'll take a stab at explaining it below:

According to Moz's Open Site Explorer, 2.97% of all links they found were nofollowed, out of 106 billion URLs and 150 million root domains. http://www.opensiteexplorer.org

All of the links from Moz.com's QA section are no-followed, as an FYI.

Wikipedia's external links are no-followed as well… and this was done as a means to reduce abuse of the system and prevent people from using WikiPedia as one giant inbound link source.

According to the nofollow WikiPedia entry:
http://en.wikipedia.org/wiki/Nofollow

… Nofollow links were originally suggested to stop comment spam in blogs, and in early 2005 Google's Matt Cutts and Blogger's Jason Shellen proposed the no-follow value to address the problem.

Generally speaking, no followed links don't help your site from an SEO perspective.

That said, Google has left it a bit open with their answer on how they handle no followed links:
https://support.google.com/webmasters/answer/96569?hl=en

How does Google handle nofollowed links?

In general, we don't follow them. This means that Google does not transfer PageRank or anchor text across these links. Essentially, using nofollow causes us to drop the target links from our overall graph of the web. However, the target pages may still appear in our index if other sites link to them without using nofollow, or if the URLs are submitted to Google in a Sitemap. Also, it's important to note that other search engines may handle nofollow in slightly different ways.

Here's what Matt Cutts of Google says about nofollow links: http://www.mattcutts.com/blog/pagerank-sculpting/
"Nofollow links definitely don’t pass PageRank. Over the years, I’ve seen a few corner cases where a nofollow link did pass anchortext, normally due to bugs in indexing that we then fixed. The essential thing you need to know is that nofollow links don’t help sites rank higher in Google’s search results."

It's possible that no followed links can actually hurt you, if you have too many of them, and you're trying to use followed vs. no-follow links within an internal link structure of your site to "Page Rank Sculpt" pages in your site:

According to Wikipedia:
On June 15, 2009, Matt Cutts, a well-known software engineer of Google, announced on his blog that GoogleBot will no longer treat nofollowed links in the same way, in order to prevent webmasters from using nofollow for PageRank sculpting. As a result of this change the usage of nofollow leads to evaporation of pagerank of outgoing normal links as they started counting total links while calculating page rank. The new system divides page rank by total number of out going links irrespective of nofollow or follow links, but passes the page rank only through follow or normal links. Matt Cutts explains that if a page has 5 normal links and 5 nofollow out going links, the page rank will be divided by 10 links and one share is passed by 5 normal links.
http://www.mattcutts.com/blog/pagerank-sculpting/

Back to Wikipedia, though…
Google states that their engine takes "nofollow" literally and does not "follow" the link at all. However, experiments conducted by SEOs show conflicting results. These studies reveal that Google does follow the link, but it does not index the linked-to page, unless it was in Google's index already for other reasons (such as other, non-nofollow links that point to the page).

I hope this helps!
-- Jeff