## via bitly blog on 9/6/11

How long is a link “alive” before people stop caring? Does it matter what kind of content it is, or where you shared it? At bitly we see a lot of links, and while every link is special, we’re learning a few general principles that we can share.

Let’s take a look at one particular story - Baby otter befriended by orphaned kittens - which was first shared by StylistMagazine on Facebook on Tuesday at 7:12am. If we plot clicks over time for this link, we see:

*Rate of clicks per 10 minutes on “Baby otter befriended by orphaned kittens”*

We can evaluate the persistence of the link by calculating what we’re calling the **half life**: the amount of time at which this link will receive half of the clicks it will ever receive after it’s reached its peak. For this link the half life was 70 minutes, which captures all the clicks between the grey lines on the graph above.

Let’s look at a second link - East Coast earthquake: 5.8 magnitude epicenter hits Virginia - , this one first shared by the Washington Post on Twitter.

*Rate of clicks per minute on “East Coast earthquake: 5.8 magnitude epicenter hits Virginia”*

While the exact details of the traffic are a little different, and the scale of the traffic to this link is much larger, we see essentially the same pattern: a fast rise, and a more relaxed drop-off. Noticeably though this link a half life of only 5 minutes: after 5 minutes this link had seen half of the clicks it would ever see.

This link is associated with a very timely event (an earthquake on the US East Coast) as opposed to the previous link (pictures of otters and kittens are clearly interesting all the time). We think that this difference in content drives the difference in dynamics of these two links. However, one alternative theory that comes up again and again is that the dynamics of the link traffic depend on where the link is posted: do links posted on facebook last longer than they do on twitter?

So we looked at the half life of 1,000 popular bitly links and the results were surprisingly similar. The mean half life of a link on twitter is 2.8 hours, on facebook it’s 3.2 hours and via ‘direct’ sources (like email or IM clients) it’s 3.4 hours. So you can expect, on average, an extra 24 minutes of attention if you post on facebook than if you post on twitter. *Distribution of half-lifes over four different referrer types. Facebook, twitter and direct link (links shared via email, instant messengers etc.) half lifes follow a strikingly similar distribution.*

Not all social sites follow this pattern. The surprise in the graph above is links that originate from youtube: these links have a half life of 7.4 hours! As clickers, we remain interested in links on youtube for a much longer period of time. You can see this dramatic difference between youtube and the other platforms for sharing links in the image above.

The graph shows the distribution of half lifes for each referrer. So we’d expect to see link half lifes of less than 20K seconds (5.5 hours) for facebook, twitter and links shared directly, and we’d be very surprised to see any link maintain significant traffic for a lot longer than 60K seconds (16 hours). But for youtube, we’d be a little surprised to see half lifes of *less than* 5 hours!

In general, **the half life of a bitly link is about 3 hours**, unless you publish your links on youtube, where you can expect about 7 hours worth of attention. Many links last a lot less than 2 hours; other more sticky links last longer than 11 hours over all the referrers. This leads us to believe that the lifespan of your link is connected more to what content it points to than on where you post it: on the social web it’s all about what you share, not where you share it!

*This post brought to you by the bitly science team! Questions or comments? Email us.*

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