LBi Search: How old are Toolbar PageRank values?

Google only updates the PageRank values seen in its toolbar every few months, but calculates new values internally much more frequently.

In this piece of research we try to answer the question "how old are the PageRank values shown when they are published?", and uncover something surprising in the process.

Please note: The web pages used in this article are used for reference only. LBi does not endorse any of the pages linked to from this article.

Google updates the PageRank values shown in the Google Toolbar every 3-4 months (and sometimes more often). However, Google also calculates the PageRank values that it uses internally much more frequently (at least daily). The PageRank shown in the Google Toolbar is therefore a "snapshot" of values at some point in time.

A commonly asked question when Google updates the PageRank values displayed within its toolbar is "How old are these new PageRank values?" - are they fresh, up-to-date values which have just been calculated, or are they several months old? Although, in general, we would recommend not obsessing about Google's green bar too much, knowing the answer to this question has several implications - for example, if you know how recent the values are, you can determine whether any recent linkbuilding activity is being accounted for within the new PageRank values.

Methodology

The methodology for this experiment is fairly simple - to know how old the values are, we need to establish what what the length of time was between pages last being given PageRank and the PageRank update. Therefore, we need to find:

Oldest mentions of PageRank update

For the purposes of finding the earliest possible date that a PageRank update was mentioned, we have looked at a number of different SEO discussion sites in order to find the earliest mention by a member of their community. We'll convert all times into British Summer Time (GMT+1) for comparison.

There are lots of other sites, but we've picked a selection of the earliest posts. The earliest one seems to be the WebmasterWorld thread, with a time of 23:12 BST on May 27th.

Newest articles with PageRank

The next step requires finding the most recent page possible which has a PageRank value. Please note that this does not mean the most recent page with a PageRank of 1 or more - a PageRank value of "zero" also constitutes a page having a PageRank value assigned to it. A PageRank of zero simply means that, on the sliding scale used by Google, the page falls into the set of pages with the lowest PageRank values. This is different from having no PageRank value at all.

The best place to look for recent pages which may have PageRank is to look for a high-PageRank, high-traffic site which is frequently updated and which uses web feeds to ensure that new pages are rapidly indexed. News sites are ideal for this. We've picked The Guardian because the website includes detailed date information, including both the original publication date and the date that the articles were last updated, whereas many other online newspapers don't include the original article publication dates.

Here are a few of the most recent articles found, along with their dates. These articles are all PageRank zero.

Hang on... what's this?

Having looked around a number of articles, we suddenly stumbled across this article, which has a PageRank value assigned (zero). The "article history" says:

"This article was first published on guardian.co.uk at 00.01 BST on Thursday 28 May 2009. It appeared in the Guardian on Thursday 28 May 2009 on p35 of the Editorials & reply section. It was last updated at 00.05 BST on Thursday 28 May 2009."

This poses something of a puzzle - here we have an article which has a PageRank score and which was apparently posted 49 minutes after the PageRank update started happening. Thinking caps on! Here are the possible causes of this seemingly paradoxical situation.

Theory 1 - The dates are wrong

This is the simplest explanation. Either the date on the WebmasterWorld thread is wrong, or the date on the rogue Guardian article is wrong.

Theory 2 - Datacenters, datacenters, datacenters

"Datacenters" - the standard fall-back answer to many a Google puzzle. As we know that different datacenters will start showing updated PageRank values at different times, it could be that the datacenter currently serving up the PageRank values that we are seeing is different to the one which first served new results to the poster who started the WebmasterWorld thread listed above.

This theory has interesting implications - given the time gap it would mean that different datacenters calculate PageRank independently of each other.

Theory 3 - Rolling PageRank update

Another possibility is that the PageRank update happens in a number of stages or over a period of time - this would mean that the update had begun when it was first noticed but had not yet been completed by the time that Google found the aforementioned Guardian article.

Conclusion

When Google performs a Toolbar PageRank update it would appear that the values are fresh and up-to-date.

Additionally, there may be an additional mechanism at work which can sometimes result in PageRank values being assigned to some pages shortly after the Toolbar PageRank update has occurred.

Got any comments about this research piece? Let us know in the comments field below!

3 Comments

Posted on 15th June 2009 at 12:09 pm by Feydakin

Appearances can be deceiving.. Especially when dealing with Google..

You left out the option that the toolbar pagerank of 0 may simply be an indicator that the page has been indexed but not yet assigned a toolbar PR yet.. Now, if those new pages had been assigned a toolbar PR of 1 or 2 or 5, you might have a case for the green bar being current.. But, I would expect that if you checked pages other than forums, which are terrible at distributing PR internally, you would see that those pages will go from 0 to some green number on the next update indicating that there may be a lag in there somewhere..

All that said, even though I think that there may be some flaws in your methodology and theory, I'm thrilled to see someone actually experimenting on things rather than pontificating mere guesswork..

Posted on 15th June 2009 at 2:38 pm by Ian Macfarlane

Thanks for the comment!

PageRank values of zero alone can't be used as a reliable indication of whether a page is indexed - take, for example, an old post of mine:

http://blog.lbi-netrank.co.uk/will-googles-new-browser-heat-up-the-second-browser-wars/

This page is PageRank N/A, but is indexed by Google:

http://www.google.com/search?q=%22Will+Google%27s+new+browser+heat+up+the+second+browser+wars%22

It also doesn't explain how pages acquire a Toolbar PageRank value _after_ the Toolbar PageRank update has begun - would love to hear your thoughts on that.

Posted on 16th June 2009 at 2:56 am by Feydakin

The last bit is actually the easy bit.. The toolbar rollouts haven't been all or nothing for at least 2 updates now.. I've seen plenty of random pages gain whitespace PR between major updates.. And with the last update at least, we were seeing toolbar changes as much as 2 weeks after it started.. Far longer than in the past..

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How old are Toolbar PageRank values?