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SEO Recommendations for Nofollow Implementation

by Virginia Nussey, July 15, 2009

Last month's feature article Matt Cutts on Nofollow and the Siloing Solution reported a recently announced change in Google's treatment of the nofollow link element. During a Q&A panel at SMX Advanced in June, Google's head of Web spam, Matt Cutts, had a discussion with the audience and the conference's chief content officer, Danny Sullivan. Matt explained that the nofollow link element "evaporates" PageRank, recommending against the use of nofollow to "sculpt" PageRank and referring to PR sculpting as a "band-aid."

At Bruce Clay, Inc., we had savvy clients who had been following the news wonder if or how it might affect their SEO strategies. Would this trusted Google representative's suggestions lead to changes on their site? There are a number of unknown elements in the equation of PageRank behavior, let alone the nofollow element's behavior. In fact, it's not known how much PageRank value is lost through nofollow links.

During the Q&A panel, Matt Cutts emphasized that linking practices are up to the site owner, and the use of nofollow is never illegal, unethical or wrong. Therefore, it's important that SEOs make an educated decision on the best use of nofollow. To help with that decision, the following is Bruce Clay's guide to search engine optimization-oriented implementation of the nofollow link element.

How the Nofollow Link Element Works Today

PageRank is Google's name for the value which passes from one page to another through a link. As a link is a show of support for the page being linked to, link value is calculated for pages on the Web as part of the search engine algorithm that calculates the relevance of a page. In the diagrams below, the concept of "points" is imaginary since Google's quantitative PageRank formula is unknown; however, the concept is useful for illustrating the principles involved in PageRank distribution.

Figure 1: PageRank passes through links, distributing link value to each page. Google has said it has a method for determining the amount of PageRank passed through each link, but for the purpose of this simple illustration, even distribution of PageRank is assumed.

Previously, including nofollow on a link would eliminate PageRank passing to that page and redistribute the flow of PageRank to the remaining links.

Figure 2: Previously, with nofollow one could eliminate PageRank transfer to select pages and condense the flow of PageRank to remaining links.

Today the nofollow element behaves differently. A nofollow element on a link evaporates the PageRank value, reducing the amount of PageRank that page can transfer through links. For the purpose of these examples, total evaporation is assumed, although it is important to note that the true level of evaporation has not been revealed by Google.

Figure 3: Using nofollow today prohibits PageRank transfer from one page to another by eliminating the PageRank value that would have been passed.

External Linking with Nofollow

Links to Untrusted Sites

The nofollow link element was originally designed as a tool to help webmasters deal with comment spam. Links are treated by search engines as a vote of trust and authority for the page being linked to. The nofollow element was originally intended for application on links within blog and article comments. Comments on blogs and articles typically include a link to the commenter's Web site of choice. People recognized that they could secure link value by linking to their sites through comments on other sites. Some chose to abuse this loophole of directing PageRank by spamming sites' comment sections with external links. To combat this manipulation, Google introduced the nofollow link element as a way for site managers to indicate a link to an untrusted site. This original use for nofollow still applies. Applying nofollow on links to unvetted third-party sites is still an acceptable use of the nofollow link element.

Advertising Links

Another valid use of the nofollow element is with paid links. Google addresses paid advertising links in its Webmasters/Site owners Help:

Buying or selling links that pass PageRank is in violation of Google's webmaster guidelines and can negatively impact a site's ranking in search results.

Not all paid links violate our guidelines. Buying and selling links is a normal part of the economy of the web when done for advertising purposes, and not for manipulation of search results. Links purchased for advertising should be designated as such. This can be done in several ways, such as:
  • Adding a rel="nofollow" attribute to the <a> tag
  • Redirecting the links to an intermediate page that is blocked from search engines with a robots.txt file

Google minces no words when it comes to paid links that pass PageRank. Any advertorial link that has been paid or bartered for should include a nofollow element or some other means of restricting PageRank distribution through the link. Purchasing links is an accepted practice that can drive traffic to a site or enhance visibility. However, at the risk of a penalty, do not include paid links on your site that pass link value.

Links in Comments

An search engine optimization strategy for links in comments may be the most significant result of the change to nofollow. As mentioned above, blogs and articles typically contain a comment section that allows readers to include links within comments. This becomes an SEO concern when faced with the following situation. If a site was to publish a blog post with high-quality, valuable information, that post would likely gain many inbound links and PageRank as a result. Such a post is also likely to receive a lot of comments. If links within these numerous comments include a nofollow element, the page will see a high percentage of PageRank evaporation. The remaining PageRank passed through links without the nofollow element is just a fraction of its value before the nofollow depletion. This may actually create a situation where posts with few or no comments could be better for passing PageRank. The question an SEO must ask is, "Why include nofollow on links if there is no benefit to the site owner?"

Internal Linking with Nofollow

Matt Cutts's Internal Linking Rule of Thumb

At the SMX Advanced panel, Matt Cutts addressed the use of nofollow on links to internal pages.

If it's an internal link, our rule of thumb is, you know, you know it, you know the source page, you know the destination page, you know that you trust both pages. I would not use nofollow in most cases.

As a representative of Google, Matt shared his informed rule of thumb with the SEO community. But a general guideline does not apply to every situation. An SEO should always evaluate links on a case-by-case basis before deciding whether or not to include a nofollow element. Ask why the link is there in the first place. Ask if it would supplement information or otherwise add value for the reader. Assessing the value and reason for the link in the first place can be helpful when deciding whether or not link value should be directed to the page.

Linking across Site Silos

In order to rank in a search engine for targeted keywords, a page must be seen as relevant to the keyword. Linking plays a role in determining relevancy, and the best quality inlinks come from pages about the same keyword or theme. Therefore it's wise to link internally in a way that adheres to theme or subject boundaries. By linking from a page about peanut butter to another page about peanut butter, the linked-to page's relevancy for peanut butter will increase.

Siloing is a strategy to construct themed sections of a Web site supported by internal linking and directory structure. In this way it differs from PageRank sculpting because the intended flow of link value is built into the architecture of the site. Siloing strategy for internal linking follows the understanding that the theme of a landing page is bolstered by links from same-theme support pages.

  1. Link from a Support Page to a Different Silo's Landing Page
  2. Link between Two Support Pages in Different Silos
  3. Link between Two Support Pages in the Same Silo

Figure 4: This diagram demonstrates linking best practices for a siloed or theme-structured site. Links 1 and 3 would not include nofollow. Link 2 might include nofollow if the themes are unrelated.

Siloing best practices generally recommend against linking from one silo support page to another silo support page because the theme of support pages might be diluted by links from unrelated pages. Any cross-silo link from a low-level page should be directed to a theme landing page because landing pages have a high volume of inlinks and will only be minimally affected by a small amount of subject dilution. Before the change in nofollow behavior, Bruce Clay recommended including a nofollow attribute on all links between support pages across theme boundaries. In light of the change, every link must be evaluated on its own merits. Evaluate each internal link by asking questions like, "Why link here?" and "What value does this add for the reader?"

Linking to Pages Not Targeted for Ranking

There are usually several pages within a site that are not targeted for ranking. Many of the pages linked from a global footer are examples of this, like a site's copyright page or privacy policy. It makes sense that SEOs would want to prohibit the transfer of link value to pages not intended for ranking. A recommended solution is to include blocks of links to pages not targeted for ranking within an iframe.

Figure 5: By including a link in an iframe, an element that search engine spiders do not associate with the page, the link does not pass link value and does not deplete the total PageRank value being passed to the remainder of links.

The iframe element removes content from the page, effectively placing it out of sight for search engine spiders. Include links to pages not intended for ranking within an iframe, but if that solution is not possible, then the use of the nofollow link element should be considered. Google has not recommended against all uses of the nofollow element, but has encouraged an educated and judicious use of this powerful link element.


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