Boosting SEO by Boosting Internal Linking: An A/B Test Case Study

Internal linking remains a powerful yet often underutilized strategy for boosting website performance. At Similar.ai, we conducted an A/B test in October 2023 on a large site to determine the effectiveness of enhancing internal links specifically to pages ranking between positions 4 and 15 on Google.

Hypothesis

Our hypothesis was straightforward: by increasing internal links to these pages, we could significantly improve their visibility and organic traffic. Pages in these positions hold high potential since even a small improvement in rank can lead to substantial gains in click-through rates (CTR) and therefore traffic and revenue.

Implementation

The approach involved doubling internal links to selected pages already performing moderately well (positions 4-15). By strategically boosting these links, we aimed to signal greater importance to search engines, thereby improving their crawl frequency and search visibility. We used the InternalLinking.io’s [Boost Internal Links](boost-links.md] recipe template to set up the recipe effortlessly, build the links and publish them.

Metrics and A/B Testing Methodology

Because the client used Botify as their site crawler and logfile analyser, we used our API integration with Botify’s Logfile Analyser. We also pulled in data through a direct connection with Google Search Console. We coupled with our A/B testing methodology to get direct feedback. This methodology holds back a % of the destination pages to which we would be linking, as a control group. Then for each metric — such as the number of ranking keywords — on each day, we subtract the number of keywords for which the control group ranks from the number of keywords for which the test group ranks to get a single figure for that metric for that day. We do that for a number of days before and after updating the internal linking and look at the averages before and after. Sometimes this is called the “difference of a difference” method for this reason.

Results

The outcomes for the site were notably positive:

  • 27% increase in pages crawled by Googlebot.
  • 12% more organic keywords ranking per page.
  • 22% increase in organic impressions.
  • 8.6% increase in organic traffic.

How to Make Sense of These Results

When my team first came up with this idea, I (Robin here!) originally said it was nonsense, because we would be removing topically relevant in-links and swapping them out for things that are irrelevant. What I saw from the results — and this is not the only result, we also have a number of other case studies — was firstly that my team was right and I was wrong!

However, the explanation could be that there are several links on any given page that are irrelevant to almost all pages yet appear consistently across most pages, i.e. the top navigation (aka the top nav). Boosting links, provided it's not done for too many pages, artificially promotes certain pages into a position akin to the top nav without altering the fundamental site structure. Typically, changing your top nav requires substantial effort, but in this scenario, we're selectively boosting pages so they appear to Google as if they're part of the top nav. If Google already has positive signals about the quality of these pages — as indicated by their existing rankings — then this additional signal reinforces their authority. That's how I've come to think about it.

Insights and Recommendations

Our recommendations for sites:

  1. Keep internal linking up to date.
  2. Prioritize linking towards pages that are missing clicks or towards pages that deliver the best user experiences.

Leveraging targeted internal linking proves not only beneficial but essential for competitive ranking improvements and overall SEO growth.