Update: This post sparked a ton of comments and debate. Read to the end for the latest updates.

Every two years, Moz runs a scientific correlation study to discover the qualities of web pages that have a strong association with ranking highly in Google. This year, for the first time, Dr. Matt Peters and the Moz Data Science Team measured the correlation between Google +1s and higher rankings.

The results were surprising.

After Page Authority, a URL's number of Google +1s is more highly correlated with search rankings than any other factor. In fact, the correlation of Google +1s beat out other well known metrics including linking root domains, Facebook shares, and even keyword usage.

Moz isn't the only one to discover this relationship. Searchmetrics, using a slightly different methodology, found Google +1s to be the highest-correlated factor they studied, and other studies have found similar results.

Here's the million-dollar question: Can Google+ activity actually help your pages rank higher?

Beyond correlation: Why it matters this time

Back in 2011, folks may remember the controversy that erupted when Moz found a similar correlation between higher rankings and Facebook activity. At the time, Google claimed they didn't use Facebook shares for ranking websites. Dr. Peters concluded that the relationship between Facebook activity and higher rankings was likely not directly related, but probably caused by overlapping factors such as links and high-quality content.

Now in 2013, there's strong reason to suspect it's different with Google+, and that the relationship between +1s and higher rankings goes beyond correlation into the territory of actual causation. (Edit: This should say "posting on Google+" instead of Google +1s. It's clear that Google doesn't use the raw number of +1s directly in its search algorithm, but Google+ posts have SEO benefits unlike other social platforms.)

Not only is the correlation for +1s higher than that for Facebook activity, but the Google+ platform has qualities that make it a far superior platform for SEO. These qualities suggest sharing content on Google+ has the potential to influence search rankings in significant ways.

Intentional or not, the engineers who made Google+ built it for SEO. Consider the factors that make sharing content on Google+ far different than sharing on other social networks:

1. Posts are crawled and indexed almost immediately

One of the original goals for Google+ was using it to power real-time search after Twitter cut off Google's firehose access to its data in 2011. Since then, Google has been using Google+ to discover new content, and many web professionals have discovered that URLs shared on Google+ are crawled and indexed very quickly.

Compare this to Facebook, where because of privacy settings and restrictions on data sharing, it's not uncommon for posts to never be crawled or indexed by Google at all.

Unlike Facebook, which hides data from Google, or Twitter, which directs Google not to follow most of its links, Google+ data is immediately and fully accessible to the company that built it.

2. Google+ posts pass link equity

Pages and posts on Google+ not only accumulate PageRank, but because links to posts are followed, they pass link equity on as well.

Using the free MozBar, you can see all of the followed links on a typical Google+ page.

When you share a link on Google+, the anchor text becomes the title of the page you are sharing. Some important things to remember about followed links within Google+:

• Only "shared" links (the links that show up beneath your post) are followed. Any external links you add withing the post body itself are nofollowed, so these don't pass any link equity.
• For obvious reasons, uploaded images don't pass external link equity. Some people like to upload a screenshot of a page and then link to it in the body of the post. While a good image may increase post popularity and click-through rate, these posts do not pass link equity.
• Certain links in your Google+ "About" page are also followed and pass link equity.

3. Google+ is optimized for semantic relevance

Unlike Facebook or Twitter, each post you make in Google+ has most of the characteristics of a full-blown blog posting.

• Each post has its own URL.
• The first 45-50 characters of the post appear in the title tag.
• Just like a blog post, entries can be long and complex in order to explore a subject deeply. Various correlation studies have show a strong relationship between longer pages and higher rankings.
• If a post is reshared, it can accumulate internal links from the Google+ platform, all with relevant anchor text.

Because of these factors, each post has the potential to send strong semantic signals to Google's search algorithm. This not only helps the post itself to rank in Google's search results, but potentially sends relevancy signals to a URL shared by the post.

What about Author Rank and Publisher Rank?

Many publishers have added Google+ authorship information to their websites in order for author photos to appear in Google search results. Another hope is that someday Google will use authorship information (and perhaps publisher information) connected to Google+ accounts to actually rank websites.

While there is no evidence that Google uses anything like Author Rank at the moment, many believe it will be here very soon. In the above video, Matt Cutts of Google suggests this is a path he'd like to see Google explore.

Taking advantage of Google+ for SEO

While there are hundreds of ways to optimize your Google+ experience, the most important activities can be summed up by these nine points:

1. Start building relationships now on Google+

It's never too late to start. Google+ is a social network. Following great people, commenting on posts, and sharing great content not only helps to increase your own influence, but it can be extremely educational as well.

2. Post share-worthy content on Google+ to attract natural links

When you share content, don't just post a link and walk away. Add additional value with commentary and relevant information.

Consider these examples of long Google+ posts. Each acts like a mini blog post and adds highly shareable, linkable context. I don't recommend replacing your personal blog with Google+ entirely, but sometimes a few lines of context makes all the difference.

3. Add Google authorship information to your online content

Adding rel="author" to your website is a no-brainer. If you guest post or otherwise contribute content to other high quality sites, ask the publisher if they will add author markup to your bio. Kane Jamison recently did this for me when I contributed content to his blog.

4. Link out to all relevant profiles from your Google+ "About" page

Think of Google+ as a primary hub of your online virtual identity. Google offers you several places to link to other online profiles, sites that you contribute content to, and simply sites that you want to share.

5. Take advantage of rel="publisher" by connecting your website to your Google+ brand page

If you are a business, organization or brand, follow these instructions.

6. Make your content easy to share on Google+ with relevant social sharing buttons

You would think everyone wants to add social sharing buttons to their content, but some folks are just stubborn. Don't be stubborn.

7. Completely fill out your Google+ profile with relevant and engaging information

The information you provide in your profile influences how you show up in Google+ search results and also plays a role in whom Google suggests others to follow.

8. Make it easy for people to add you to your circles

Use Google's easy-to-create badges, or create your own to place on your own online profiles so that others can easily add you to their circles.

9. Make your posts public
Posts shared privately don't pass the same juice as publicly shared post. For SEO purposes, you likely want your posts spread as wide as possible. Philipp Steuer made this great Google+ infographic simplifying the complexities of who sees your posts:

Google+ Infographic by Philipp Steuer, used with permission

Additional resources for success

Entire books can now be written on using Google+ to boost your SEO efforts. In reality, there are exactly 3 articles that contain 99% of everything you need to know:

• Google Plus SEO: Everybody Talks About It – How Do You DO It? by Mark Traphagen
• Google+ SEO by AJ Kohn
• 10 Dead Simple Tips to Take Advantage of Google+ for SEO

What's your favorite Google+ tip? Please share in the comments below.

Update:

This post caused quite a bit of controversy. Matt Cutts of Google responded to this thread on Hacker News to imply +1s aren't used directly in Google's algorithm.

While I take Matt at his word that Google doesn't use raw +1s to rank webpages, the evidence seems to suggest Google+ posts do pass other SEO benefits not found easily in other social platforms. If this is not the case, I'm hoping Google will clarify.

Mark Traphagen said it best in this comment:

It is not the +1's themselves that are causing the high rankings of posts but the fact that most +1's on a site result in a shared post on Google+, which creates a followed link back to the post. It's instant organic link building.

The point is not to go out and accumulate a bunch of +1s.The point is, and the evidence seems to suggest, that earning a link on Google+ is like earning any other type of editorial link, and these links have actual value with real benefits.