This is guest post by Dan Zarrella, a social media marketing consultant. You can follow him on Twitter here.

While some people have said that Digg has begun to lose its relevancy since the recent algorithmic changes, I believe it still represents an incredibly rich resource for studying social media and how stories and links spread throughout the web community. Once a link "goes popular" and is listed on Digg's homepage it is seen by many and perhaps even a majority of web geeks. Very often these readers have their own blogs, and if they like a story they may blog about it or link to it. This is why many webmasters yearn to be Dugg -- not for the first wave of traffic, which is often substantial but hard to retain, but for the viral wave of traffic and links that comes as a result.

Plenty of research has been done via Digg's API to study how stories make the homepage. We know the best time to submit to Digg, and we know the best categories and types of stories (e.g. top lists, how-tos and stories about Digg), but what has never been studied before is what happens after a link goes popular.

Digg's algorithm can be gamed just like any other, so we often see sub par stories hit the homepage, but low-quality stories rarely receive any substantial amount of links once they're made popular. It takes real, quality content to induce savvy social media users and bloggers to link to a story.

So I decided to study this effect: what types of stories get lots of links after going popular? I created a database of 33,000 of the 39,000 stories that made Digg's homepage in 2007 and, using Yahoo!'s API, I tracked how many external links each URL had pointing to it. Then I analyzed a number of factors that could influence the number of links a story gets and wrote a report with my findings.

I'm publishing my Link Attraction Factors (PDF) report exclusively for the first time here on ReadWriteWeb and I'd love to hear everyone's thoughts and comments. The report is available as a free PDF file.

Once I realized that the occurrence of certain words in a story's title or description can have a potentially large positive or negative effects on incoming link accumulation, I created two tools that leverage my database.

The Keyword Tool analyzes a specific word or phrase and returns the average number of links a story mentioning that keyword got in 2007. While the Title Check Tool analyzes an entire title string and shows you which words tend to increase links and which tend to decrease links. These tools can be used by webmasters or social media consultants to help them tweak their copy for optimal social media link attraction, or by other researchers looking to expand on my work.

I plan to expand some of this data for future reports, including by looking at social sites other than Digg and incoming link data sources other than Yahoo! Again, I'd love to hear all of your ideas in the comments.