A Good Alt is Better Than a Bad Anchor

A short while ago, I set up a small test in order to determine the value of an alt attribute, in comparison with a title tag and anchor text. Although quite a few link building text books advize you to avoid using image links, and the results for this subject in the Link Value Factors were inconclusive, I have always believed that optimized image links can be nearly as valuable as regular text links.

Tests in the past, as well as experience, have showed us that if you compare a text link with an optimized anchor text with an image link with the same words attached as alt attribute, the page where the anchor text link points to will rank higher. This means that there’s no need to determine if a text link is “better” than an image link, but it still is worth to test the differences and smaller factors underneath. Nothing big, but useful enough to run a test.

The test

For this test, I have set up a page on a new subdomain of an existing domain. Unfortunately, I can’t share the domain, nor the exact keyword combination, because this particular test has already been (accidentally) terminated. Let’s just say I deleted a file I wasn’t supposed to :)

First, I wrote 6 different texts that were optimized for a combination of 2 different keywords ([KW1 KW2]). Both of these keywords return results in Google, but if you add them together in a single query, zero results show up. All texts were unique, but similar in layout and optimization technique. The keywords where the pages have been optimized for were in the exact same locations (word-wise) on every page.

Then, I set up a page with 6 different links. Three of these links were image links, and three were text links. For the images, which all had non-keyword filenames, I used different images of the same size. Although I do know that Google uses link order in the process of link valuation, I left this factor out on purpose.

The positions of the links on the page were:

1. An image link without an alt attribute or title tag.
2. An image link without an alt attribute, but with a [KW1 KW2] title tag.
3. An image link with a [KW1 KW2] alt attribute, but without a title tag.
4. A text link with a non-keyword (ie click here) anchor text.
5. A text link with a partially optimized (more about KW1 here) anchor text.
6. A nofollowed link with [KW1 KW2] anchor text.

After all pages had been uploaded, I added two links for indexation and let the test soak for about four months. During these months, all results were constantly (every week) monitored to see if the rankings were stable. Just to be sure, I also set up a control test, but that one was slightly different from this test.

The hypothesis

Like I mentioned, I do know that the order of the links matters. Although the differences are small, it does matter if you’re the first link on a page or the 217th. Because it is extremely difficult to set up a page in a way that it distributes an equal amount of link strength to each link, I decided to list the links in an order that would make any positive result clearly visible. The -in my opinion- least valuable link was listed first. I expected Google to list the pages in the following order after searching for [KW1 KW2]:

1. An image link with a [KW1 KW2] alt attribute, but without a title tag.
2. A text link with a partially optimized (more about KW1 here) anchor text.
3. An image link without an alt attribute, but with a [KW1 KW2] title tag.
4. An image link without an alt attribute or title tag.
5. A text link with a non-keyword (ie click here) anchor text.

I assumed that the nofollowed page would not show up, but I included the page as an extra control measurement.

The results

About 3 months after the test was set up and the rankings didn’t change in two months, it was time to end the test. A search for [KW1 KW2] made Google only list two URLs in the results. Only page 1 and page 3 showed up. After clicking on ‘repeat the search with the omitted results included’, three more pages showed up in an order that was slightly different from what I expected. The optimized title tag link (#2 in the original set-up) ranked above the partially optimized anchor text link (#5 in the original set-up). As expected, the page where the nofollowed link pointed to, didn’t show up.

1. An image link with a [KW1 KW2] alt attribute, but without a title tag.
2. An image link without an alt attribute, but with a [KW1 KW2] title tag.
3. A text link with a partially optimized (more about [KW1] here) anchor text.
4. An image link without an alt attribute or title tag.
5. A text link with a non-keyword (ie click here) anchor text.

The control test did not show any different results.

The conclusion

The conclusion of this particular test, is that an image link with an optimized anchor text is more valuable than a text link with an anchor text that is not optimized very well, in terms of ability to pass relevance.

An image link with an optimized anchor text might be more valuable than a text link with an anchor text that is not optimized very well. Because of the small difference in rankings and because of the order the links were placed in, a new test should be set up in order to

While lots of folks try to avoid image links (image based navigation included), this is absolutely not necessary. Depending on the anchor text possibilities, I would even prefer image links over text links in some cases. When you have an imaged based navigation with links to ‘Home’, ‘Services’, ‘Products’ and ‘About’, for example, you can add extra value by making the alt attributes more descriptive. This test shows that an optimized alt attribute (‘SEO Services’) might be better than a not so optimized anchor text (‘Services’).

The side notes

Setting up an SEO test that is 100% valid remains extremely difficult for several reasons. I probably made a small mistake somewhere while setting up this test, but I do think the results are pretty valid.

Please note that this test only included links to internal pages. It might be that image links that point to external pages are being treated differently by the major search engines. Also, the image format that I used was not a standard format. Google might value a link from an image of 70×15 px different than a link from an image of 468×60 or 250×250 px. This however, can (and will) be tested in a different set-up.