A look at the Digg “Story Deserves Freshness” algorithm

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  • June 25, 2008
Patrick Altoft

Patrick Altoft

Director of Strategy

Google uses an innovative algorithm called Query Deserves Freshness or QDF to make sure that new pages are given top rankings for queries that see a sudden spike in traffic.

This ensures that users searching for fast moving terms such as earthquakes and breaking news stories are given the most relevant information. The algorithm looks at things like search query volume, blog post volume and news search volume to determine whether they need to be showing new pages or old pages.

Digg has a similar system for promoting breaking news stories to the homepage. Most of the time a story takes 24 hours and perhaps 200 Diggs to make it’s way through the system to the homepage but whenever a really hot story breaks (such as a new iPhone from Apple) you can be sure the Engadget coverage will hit the homepage with around 35 Diggs in the first hour.

Why does this happen and how can we use this to help our stories on Digg?

The obvious factor is the number of votes the story attracts in a short space of time. Getting 100 natural votes in a couple of hours will almost guarantee the story hits the homepage. However when we see posts going hot in an hour or two with just 35 Diggs it’s clear the algorithm is heavily weighted towards something else.

My belief is that Digg takes the source of the votes into account and gives much more weight to certain types of vote. The Digg team likes users to believe in the wisdom of crowds and the notion that all votes are equal but any long term user knows that some votes are more equal than others.

The different types of votes, in order of value:

  1. Attempted submission of a story that is already submitted
  2. Voting from the Upcoming queue
  3. Clicking the Digg button on the source website
  4. Navigating to the story from inside the Digg website (eg a profile page)
  5. Clicking on a direct link to the Digg story (eg email, IM etc)

Note that clicking on a direct link from a known spam source such as a webmaster forum will probably get your vote automatically devalued.

Of course the source of the vote isn’t the only variable – the authority of the user has a big influence on the algorithm too. In general the more votes a story gets from powerful users the greater it’s chance of becoming popular.

However this isn’t always the case because a lot of power users rely heavily on votes from their friends, both inside and outside Digg. If a user regularly gets votes from a particular group of people either by IM, sending shouts or by email these votes will be devalued.

Conclusions

From this we can conclude that several factors can come together to create a “perfect storm” situation that causes a story to leapfrog the rest of the submission queue and hit the front page within an hour.

This situation appears to be perhaps 20-30 users who are not known for voting each others stories all trying to submit the same story within a short timescale. This combined with another 20-30 votes from the Upcoming queue and maybe a Digg button on the article page can propel the story onto the front page within a very quick timescale.

Photo credit Matthew Fang

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