Halflife by Topic

At bitly we extract the topic of each page whose URL gets shortened using our service. We decided to see how the topic of the page affects how quickly the page gets consumed after publication. To measure the speed of consumption, we use a metric we call the ‘halflife’ of the page.


We find the ‘halflife’ of a link by calculating the time from the first click on a link to the median click - this means we line up all the clicks on a link in time order and then find the time of the middle click and subtract from it the time of the first click. This is the amount of time it took for a page to receive half the traffic it’s ever likely to see.

We like this way of thinking about the consumption dynamics of a page for two reasons. It captures both the large initial burst of interest on a page as well as the long, heavy tail of readership in the latter stages of a page’s life cycle.

Don’t Blink if You’re Watching Sports

In general, we found that topic doesn’t have a large measurable effect on the halflife of a link, with one notable exception: sports. In this case, a large proportion of the links have a halflife of less than 200 minutes, which means that a page about sports have a much shorter amount of time to capture their audience.

By contrast, as shown in the plot below, pages about business are much more likely than sports to have a longer half life, and so publishers of this material can expect halflives of up to 500 minutes.

Figure 1: distribution of halflife by topic. Sports pages, shown in orange, are much more likely to have a short halflife (<200 minutes) whereas Business pages, shown in purple, have a more even distribution of short and long halflives.

It shouldn’t come as a surprise that sports fan are only interested in the freshest news, but it does come as a surprise that so many other topics are surprisingly consistent.