In August, 2005, SEOmoz launched the first series of ranking factors. We asked a dozen folks in the SEO world to vote on the importance of over 100 unique factors surmised to be part of the search engines' ranking algorithms. Today, we've released a new version that addresses many of the issues that frustrated users of the first version and updates the series to modern times.

A few of the major changes include:

• We've gone from 12 contributors (plus myself) to 35 participants, spanning a wide range of specializations, geographies and even hat color :)
• The new factors list is specifically geared to Google - we'd love to include all the engines, but it's not fair to ask a voter which factor matters most at all the engines when they clearly have different preferences.
• In addition to the factors themselves, I've asked a few forward-looking questions with multiple choice answers and recorded our panelists' answers
• Rather than attempt to list 100+ factors, I've instead opted for readability and usability. The new factors includes just 55 unique criteria, many of them encompassing several pieces of ranking data. Overall, I think this format is far more valuable for those who have practical, rather than scholarly interest.
• Jeff has updated the design significantly and added some additional functionality to the piece (drop down comments in particular).

One of the most fascinating items for me to observe is the change of the Top 10 most important pieces as ranked this year vs. 2005.

Top 10 Ranking Factors in 2005:

1. Title Tag (4.57)
2. Anchor Text of Links (4.46)
3. Keyword Use in Document Text  (4.38)
4. Accessibility of Document (4.3)
5. Links to Document from Site-Internal Pages (4.15)
6. Primary Subject Matter of Site - (4.00)
7. External Links to Linking Pages (3.92)
8. Link Popularity of Site in Topical Community (3.77)
9. Global Link Popularity of Site (3.69)
10. Keyword Spamming (3.69)

Top 10 Ranking Factors in 2007:

1. Keyword Use in Title Tag (4.9)
2. Global Link Popularity of Site (4.5)
3. Anchor Text of Inbound Link (4.4)
4. Link Popularity within the Site's Internal Link Structure (4.1)
5. Age of Site (4)
6. Topical Relevance of Inbound Links to Site (3.9)
7. Link Popularity of Site in Topical Community (3.9)
8. Keyword Use in Body Text (3.9)
9. Global Link Popularity of Linking Site (3.7)
10. Topical Relationship of Linking Page (3.6)

The biggest mover is clearly "Global Link Popularity" - which fits very well with evidence we've seen of sites like Wikipedia and other authorities dominating the SERPs. It's also interesting to see "Primary Subject Matter of Site" dropping out, another endorsement of large authority sites ranking for terms and phrases often unrelated to their primary topic. Internal link popularity, anchor text and topical popularity have all remained relatively consistent, but "Age of Site" is a new entrant to the top 10 (despite my personal opinion that it's been important for the last 3 years).

For me, this is one of the most valuable documents on the web for determining how to approach an overall SEO strategy. While the factors may not be perfect, they give a remarkably concise and trustworthy view of what makes a site rank well at Google. I hope you all enjoy it as much as I have - please add your thoughts in the comments!