There has been some buzz lately from bloggers worried that CommentLuv leaks link juice. Researching this question became more than just an academic question for me, as I have been seriously considering about adding CommentLuv to my blog, Internet Marketing Remarks.
What is CommentLuv?
CommentLuv is a plugin that places the title of a recent blog post of a commenter under their comment on a blog article. This can be useful in gaining more comments, as commenters judge they are getting rewarded. It can also lead to a blog receiving spammy comments.
What is Link Juice?
Link Juice is a term that refers to how much search engine ranking benefit a link passes along. Based on the original Google algorithm published in 1998, if you had a page with eight PageRank points and four outgoing links, each of the four links would flow two points of PageRank Thus, if it was still 1998 and no changes had been made to the Google algorithm, then having lots of outgoing links to commenters’ posts would probably “leak” link juice. These links to commenters’ posts would have been harmful because they would reduce the link juice passed internally to other pages on your blog. However, the Google algorithm has undergone massive changes in the past 13 years. Position of links on a page is an important factor in how much link juice gets passed, and the comments at the bottom of the page carry much less link juice value than links in the first few paragraphs of an article.
Does CommentLuv Leak Link Juice?
If blogs leak link juice due to CommentLuv, a likely outcome would be that not as much link juice would be passed along via internal links to other pages on the blog. If this were the case, the link authority of the domain would be reduced as a ratio of the link authority of the blog home page. Blogs that do not use CommentLuv can serve as a control group in determining if there is a change in the juice is being passed by internal links and if there is an impact on the domain link authority.
Based on an analysis of home page authority and domain authority utilizing Open Site Explorer, CommentLuv does not seem to be leaking link juice
The chart below shows that the ratio between Home Page Authority and Domain Authority for a selection of 10 blogs that utilize CommentLuv is 87% versus 88% for 10 blogs that do not use it. Given the sample size, 1% is not a statistically significant difference.
Blogs That Feature The CommentLuv Plugin
Blogs That Do Not Include the CommentLuv Plugin
(The control group was selected from blogs featured in 50 Most Influential People in Blogging.)
Importantly, the conclusion that CommentLuv does not leak link juice based on this finding requires two major and potentially flawed assumptions:
- The Link Authority results were obtained via SEOmoz’s Open Site Explorer tool. Using Link Authority to determine link juice leakage is only valid if SEOmoz has effectively backward engineered the Google algorithm. An article by Rand Fishkin supports the case that there is a correlation between Link Authority, Google rankings and PageRank. My own testing also seems to support an argument that the correlation is solid.
- I have assumed that if CommentLuv enabled sites leaked link juice there would be a drop in domain link authority versus home page link authority. If link juice is leaking away to the sites’ of commenters, then the internal links of the CommentLuv enabled blogs would not be passing along as much link juice and the domain as a whole would suffer a loss of link authority. The fact that the ratios are essentially the same for both types of blogs seemingly indicates that link authority in not being leaked.
Additional support for a conclusion that CommentLuv does not leak link juice is provided by the strong ranking on search engines for competitive term for sites that feature the CommentLuv plugin.
As a caveat to my conclusion, I did not control for whether or not the blogs used no-followed tags. However, based on Google spam sheriff Matt Cutt’s repudiation of page rank sculpting and no-follow tags as a technique for hoarding link juice, this may not have had much of an effect on the results. For reference, CommentLuv can be set to either no-follow or follow. Since no-follow tags limit the link juice passed along by a comments, they cut down somewhat on the incentive for the insertion of spammy comments.
(Updated 1/21/11) However, it is probably appropriate to be cautious about turning off the nofollow tag on comments. While this issue needs further investigation, there is reason for concern that Google PageRank penalties could result from links to ”bad neighborhoods” if the nofollow tag is turned off. For reference, the default setting in WordPress, Drupal, and Joomla is for the rel=”nofollow” tag to be included as part of the hyperlink to the sites of commenters. Google Webmaster Tools recommends “If you can’t or don’t want to vouch for the content of pages you link to from your site — for example, untrusted user comments or guestbook entries — you should nofollow those links. This can discourage spammers from targeting your site, and will help keep your site from inadvertently passing PageRank to bad neighborhoods on the web.”
Based on the results of my study, I’ve added CommentLuv to my blog as I’m reasonably confident that it does not leak link juice.
About the Author – Randy Pickard has been optimizing website for search since 1996. Randy is the editor of Internet Marketing Remarks and President of Exceptional Shopping Sites. He recently launched Shopping Basket Plus, a supplier of shopping baskets to retail stores.