One of our members recently reported that Yahoo was recommending separating the keywords in your meta-tag using commas. As we know from experience, the official representatives of the search engines don't always give us the best advice as it pertains to ranking. We decided to check out this claim using a statistical analysis to find out if using commas in your keywords meta-tag had any affect on ranking on Yahoo. We also studied Google to see if there was any affect on that search engine.
Here is the methodology I used to answer this question. I gathered the results of the queries naturally performed last month by myself and four associates using Yahoo and Google. I then fetched the pages and looks at any keywords meta-tags on the listed pages. I tallied the results for the first 8 rankings on both Yahoo and Google (keeping the results separate) and then converted them into a percentage of the total results for each search engine.
Here is the graph showing Google and Yahoo results:
http://searchenginegeek.com/graphs/df03.gif
(Note to webmasters: Feel free to hot-link to the above graph or even copy it to your own site. Also feel free to remove this note.)
The X-axis shows the ranking (from #1 through #8) of the search engine results in the study. The Y-axis shows the percentage of domains that contained commas in the keywords meta-tag.
The first thing to notice is that roughly 40%-50% of all pages in the first eight rankings have a keywords meta-tag with commas separating the keywords. That really doesn't tell us much about the ranking of such pages though, only the general distribution of pages with commas in a keywords meta-tag in the top 8 results. Still, I was surprised that the percentages were so high. For several years, the general consensus was that no significant search engine even utilized the keywords meta-tag (this was before Yahoo switched from service Google results to their own). With that general consensus, I expected that a vast majority of sites had dropped using this meta-tag. However, over 40% of top ranked sites continue to persist in their use. I find that interesting.
The next thing to notice is that Google showed absolutely no ranking difference between sites that use commas in the keywords meta-tag vs. sites that do not use commas in the keywords meta-tag or have no keywords meta-tag at all. The ranking correlation was an exact zero on a scale of -100 to +100.
Yahoo's ranking correlation was a -28 on a scale of -100 to +100 for pages having commas in the keywords meta-tags. I generally treat results between -35 and +35 as insignificant (don't not affect ranking or the affect on ranking is small to insignificant). However, since Yahoo recommended using commas, I did find the -28 result interesting. Once again, it appears that the official representatives of a search engine are steering us wrong (at least for purposes of ranking higher on their search engine). This result indicates that using commas is either insignificant or if there is any significant affect... it is NEGATIVE!
Advice: Don't use commas in your keywords meta-tag. Pages that use commas in the keywords meta-tag do NOT rank higher and there may be a slight negative affect on Yahoo.