One of the attendees on my recent Bristol SEO training course noted that she had just done a back link trawl using www.alexa.com and found links to her website from blog post comments. She wondered if these links contributed to her PageRank? The short answer is that it’s unlikely. Take a look at the following screenshot. It shows a link in the comments section of a WordPress blog.
Notice that the blue highlighted section has an attribute that says rel=”external nofollow”. This command instructs Google to ignore the link and blocks any PageRank that might flow to the target. The rel=”nofollow” attribute is one of the major reasons for discrepancies in the Google Link Count and the Alexa Link Count. Google does not include nofollow links were as Alexa does. As an example, I run a small website and according to Google Webmaster Tools it has 10 links. Alexa reports just 1 link. From this we can assume that Alexa never found the other 9 links. Another site I run has 23 links according to Google Webmaster Tools and 170 links according to Alexa. This is most probably due to nofollow links and links form websites that Google considers poor quality or spammy. From this you can see that there is no sure way of detecting good quality links other than via the Google Webmaster Tools control panel.