Hilary Mason, Chief Scientist at bit.ly, a large link shortening service, has done an analysis on some of their link data to get an idea of how long links remain “alive” or “popular”. The measure was to look at 1,000 links and graph the number of hits that a link receives over 80,000 seconds (almost a day), and then determine the point over that period where half of the total number of hits were received. From the post
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.
Running the data yielded the following graph, showing a strong power law for Facebook, Twitter and direct links (links shared via email, and instant messengers), but a delayed curve for YouTube.
What Mason computed would more accurately be called the median rather than the half-life, since she is interested in the first point in time that divides the total number of hits for the period into two roughly equal sets. More discussion on this point is given in the comments to the post. The conclusion from the post
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!
A while back I posted on the half-life of patching vulnerabilities being 30 days and there we probably have confusion with the sample median as well. I also noted the attrition for my own links in Shark Fin posts.