A recent change at Google had a lot of people in the SEM industry puzzled. Last Thursday, the tool that measures the PageRank Google assigns a page or document went blank, showing a gray PR0 for every site in its index. The bar remained blank until early this afternoon when PageRank values became visible to searchers on the east coast of North America. It is expected to be fully active everywhere in the next 24-hours.

Even after Google warned consumers that the Google PR Toolbar should be viewed for entertainment purposes only, the handy gray to green bar produced some of the most widely quoted website statistics. When the only stat it showed was a universal gray bar, webmasters worried. Gray bars are generally associated with a site being dropped or penalized by Google. When they found out that everyone was seeing gray and that they had nothing to worry about, most seemed to miss the tiny status meter.

For over three years, the PR Toolbar provided a relative view of the importance of a website in Google’s view on a sliding scale of 1 – 10. When a site was assigned a high PageRank score it tended to perform better in Google searches and links from that site were assumed to be stronger than links from a site with a lower PageRank score. As explained at Google’s PageRank page (linked above), “PageRank relies on the uniquely democratic nature of the web by using its vast link structure as an indicator of an individual page’s value. In essence, Google interprets a link from page A to page B as a vote, by page A, for page B. But, Google looks at more than the sheer volume of votes, or links a page receives; it also analyzes the page that casts the vote. Votes cast by pages that are themselves “important” weigh more heavily and help to make other pages “important.””

In other words, links from sites with high PageRanks could be considered gold for webmasters working in highly competitive sectors. After basic keyword analysis, Google’s rankings are based primarily on the value of links directed to a document. Over time, Google has improved on its ability to analyze the relevancy of incoming links and the value of information provided by the Toolbar has decreased significantly.

Nevertheless, many webmasters and SEOs continue to obsess on PageRank values assigned to their sites. PageRank continues to be a favourite topic at many search related forums. Businesses selling links based on Google PageRank emerged about three years ago, forcing Google to add more weight to document and link histories when considering the value of links. Tools to measure PageRank were built into Firefox extensions, site rank checkers and link analysis software, putting a larger load on Google’s servers. Massive consumer interest might in fact be the direct cause of the Toolbar’s downtime.

According to a post from Webmasterworld’s GoogleGuy (a Google employee), “I talked to a few people and there was some new infrastructure that was swapping in. They expect normal toolbar PageRank display to resume in a few hours–no need for concern.”