Users clicking onto videos links sent via Twitter spend significantly longer watching those videos than those arriving from Digg or Facebook, according to a new study by video stats site TubeMogul.

The methodology (below) seems fairly robust, so it may offer a real insight into current Twitter usage: On Twitter you can follow interesting people, not just your friends.

The disparity of Twitter vs Digg is quite striking, with people spending less than a minute on the Digg-referred video. Perhaps this is because a link recommended on Digg could be posted with a misleading headline by someone you do not know.

With Facebook, you are more likely to know the person posting the link, but maybe your friends don’t post interesting links. Facebook video links get one minute and 14 seconds of viewing.

For video links shared via Twitter, however, users spend a full minute and 38 seconds watching them.

Why? Because Facebook focuses on who you know, while Twitter focuses what you know.

Twitter allows you to follow the millions of interesting people whom you do not know. These people will share great information, but you may never meet them.

Facebook, on the other hand, limits your feed to a more restricted circle. This may be interesting for intimate news (“Maisie is getting engaged”), but the open nature of Twitter allows you to peruse the best written feeds in the world on any topic you like.

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TubeMogul’s Methodology: For a three-month period, we recorded a sample of 6,763,690 video streams referred by links from Digg, Facebook and Twitter. For example, if someone sent a Tweet saying “check out this video” and provided a link, we tracked any viewers that clicked the link. The streams hail from six top video sites that average in the billions of streams per month (due to partnership limitations, we cannot disclose which sites).