Dr. Garcia has updated what is probably his most famous research work in SEO circles - the Keyword Co-Occurence and Semantic Connectivity paper. In the paper, Dr. Garcia notes the mis-use by some in SEO of the C-Index calculation and warns against using it as a fully reliable and comparable measurement in the major commercial search engines.

The updated paper is also significantly more clear about the uses for C-Indices and how they apply to the field of search engines, IR & SEO. The paper has this to say on the reasons to use the measurements:

Why we should care about co-occurrence? Some compelling reasons are:

• Keyword-brand associations.
• Brand visibility across search engines.
• Co-citation of products and services.
• Search volume co-occurrence (Co-Volume).
• Positioning of documents in search results pages (SERPs).
• Keywords research and terms discovery.
• Analysis of seasonal trends.
• Design of thematic sites.

The C-Index tool here at SEOmoz will be undergoing some changes, particularly to the use parameters and advice based on this new information.

If you are still a bit confused and are searching for a very good way to put this information to use, take your primary keyword phrase and find the ten terms most closely related, then use c-index measurements to rank them in order of highest to lowest. Be mindful of synonyms, polysemy, invented terms and other wildcards that can throw off your data. When you've compiled the list, you should be able to say with some certainty that those terms at the top will prove to be better anchor text, better page titles and better pages to search for links from to improve your site's rankings. The Related Terms tool is designed to help make this process less time-intensive.

NOTE: The tools mentioned here at SEOmoz are still under development and may be non-functional for several days to come. Sorry!