Collaborating with over 70 plusone account holders, Keesjan Deelstra and Gerard Klein set out to find out what the effect of Google +1 was on impressions, rankings and traffic and other positive effects it might have.
The study was by no means perfect in it's execution and the results seem to be so staggeringly good as to invoke a degree of skepticism, but the overall observations are sound and above all, interesting.
SEO Effect candidly acknowledge the limits and flaws in the experiment. To use their own words "on the Internet, there is no such thing as a lab-test" so the effect of +1 votes on ranking cannot be measured in isolation of seasonal trends, geographical differences, a sudden critical mass of users and Google's own tests of the +1 system. Factors such as tweeting the experiment to get more users involved and the natural personalization factors that come into play as a logged in Google user also may have skewed their test results.
SEO Effect measured the impact of +1 on three different pages of their own website. They tested the effect on the home page, a static tool page and their blog post page, announcing the experiment.
'Plusone' account holders were sourced through the blog post which they were encouraged to share on Twitter and announce their engagement in the experiment. Results were recorded over 30 days and snapshots were taken after certain milestones in the number of plushness gained.
SEO Effect Homepage - no increase in search impressions but saw an average increase of 24% in visibility across a range of keywords. Static tool page - saw an increase in clicks and an average increase of 20% in visibility across a range of keywords. Blog post page - saw an increase in impressions and clicks but results were discounted as the page was new to the Google index and heavily promoted via social media.
301 redirects do not transfer +1 data to new URL - As SEO Effect note, although 301 redirects are often used during site migration, particularly as a means of preserving good rankings during a migration progress, it might make sense not to allow +1 data to carry to new URLs because such a system would be open to abuse. For example, many +1's could essentially be farmed on one URL and then pointed to a new URL to boost different content.
+1 annotations seem to have a positive effect on search impressions - As you have to be logged in to see +1 in search results, there is a tendency for personalization and search history to come into play. As a result, +1'd selections tend to have a higher position when users re-visit earlier searches.
Also, as would be expected and as is currently the case for 'shared on Twitter' results, +1'd results are highly visible in the social circle results which tend to appear mid way down the SERPs page.
+1 annotations have a positive effect on the visibility of a search result - Users from your social circle who "+1'd this" provides another visual cue to the user which may increase clickthrough rates (CTR) on that listing. This would bear out research from Verisign and Xmarks who have also reported increased clickthroughs by overlaying trust factors into SERPs.
The SEO Effect Google +1 Experiment whitepaper, concludes that the Google +1 button saw a 20% increase in rankings which led to a corresponding lift in Clickthrough rate (CTR). Whilst in my opinion, right now, the test on rankings is too fuzzy in it's implementation and was not competitive enough a target phrase to say anything truly groundbreaking about the impact on rankings, the real merits of the study are in the impact of trust factors on CTR. The SEO Effects findings broadly match up with Verisign's findings that their "secured by Verisign seal" caused a lift of 18% on CTR. It seems likely that this is the message Google will most likely push about +1 swell. Google have never liked talking about how to improve rankings per se, so will instead push the concept that +1 will improve clickthrough rates in organic listings, which is merit enough for webmasters to adopt it.
With that in mind, it seems fairly safe to hypothesize that integrations with Google Webmaster Tools will show how +1 increased CTR on URLs in organic searches, whilst AdWords will show CTR increases where ads are displayed to users with a +1. This latter integration will naturally provide incentive to advertisers and webmeisters as higher CTR means lower cost-per-click (CPC).
Therefore, I guess a Google Analytics integration will work on accounts that have integrated Google AdWords data, but may also show a new event similar to webmaster tools. It would be cool to see if +1 data in Google Analytics can be mapped against visitor loyalty and recency statistics. It would also be nice to see if incoming search traffic can be mapped to users who only saw it as a +1 listing.
Regardless of what we might see in terms of tools integrations, the key takeaway from the SEO effect analysis, for me, is that it really is logical to expect a rankings increase from +1'd results.
Even though Google has never officially said that it tracks CTR in organic search listings, experienced SEOs know that does seem to be a correlation. Equally in a fairly roundabout way Google has recently acknowledged that user data is playing more of a role in organizing results, something many have suspected is going on for years.
Either way, if a +1 increases clicks, it naturally follows that sites will see a boost in search position (even if they don't show up as +1'd to non-logged in users) aswell as the automatic boost from appearing in social circle results.
I would say that it's a happy coincidence for Google that those SEOs who really want to estimate the impact of +1 on their organic rankings are best off jumping into an AdWords campaign to calculate the influence of +1 on CTR and most easily gauge the reach of the social circle of their target audience. This is particularly great news for PPC agencies who have been looking to bolster their SEO pitch to clients and offer a more integrated service.
I would say it's time for SEO experts and PPC experts to start teaming up. That is, if you haven't already. Would you agree?