A report from search engine optimization firm BrightEdge found that while only about half of the top 10,000 websites add Tweet buttons to help their visitors share content, those that do can see much more exposure than those that don’t.

The firm’s study analyzed 4 million randomly selected tweets in August, 2011 and found that the average number of Twitter mentions for a web page was seven times higher for pages which included Twitter’s Tweet button. The button allows visitors who already have a Twitter account to immediately publish a link to the site to their followers with just a couple of clicks.

There is a definitely a correlative relationship between adding a Tweet button and getting more exposure, but the study doesn’t establish a causality. That said, our own experience shows us that this is the case.

BrightEdge also found that fewer than half — about 42% — of the top 10,000 websites actually have these Tweet buttons. The firm didn’t explain by what measure these websites were in the “top 10,000,” but the report suggest that these sites are missing out on potential traffic or revenue.

Facebook sharing buttons were more common; about 50% of the top sites featured them. That’s a small gap between Facebook and Twitter, given that Facebook has nearly four times as many members as Twitter.

Upstart social network Google+ and its +1 button trailed behind, with 8% of the top sites including it, and LinkedIn came in fourth with 4% of sites. You can view the full report at BrightEdge’s website, but you’ll have to provide some contact info to the company to get it.

[Via: All Twitter, Image credit: Norlando Pobre]