CollaborativeRank is an interesting service that builds on the del.icio.us database. They provide bookmark search, a ranking of popular bookmarks, and they attempt to find connections between the things people store in their del.icio.us account and their area of expertise. It's the last feature that I find the most interesting. While it disguises as a ranking of users, its main promise is that it could help you find experts on arbitrary fields.
During the last couple of weeks I've been watching my rank, and while I wouldn't necessarily agree with its estimation of my expertise it's still interesting to watch.
At the time of writing I'm 120th on CollaborativeRank's list of del.icio.us users.
When I first bookmarked their page on 2005-10-09 my main area of expertise according to this system was "wifi", which seemed a little strange as I don't know anything about this topic. Even more odd was the fact that I had only four bookmarks tagged with "wifi", but apparently the number of bookmarks is not as important as what it is that you are actually bookmarking.
My current areas of expertise, as you can also see on the screenshot above: xml, mining, validation, geo, xslt, politics, wireless, wifi, vpn, blogs. Note that CollaborativeRank, for reasons unknown to me, split my "datamining" tag into the meaningless words "data" and "mining".
Note also that I have only one (1!) URL each under the tags "xslt", "wireless" and "vpn", yet I'm already deemed an expert on these topics. Isn't that strange? Not so, as you'll see.
When you think a little about it their algorithm seems quite straightforward. Extract from their FAQ:
The overall ranking [...] does provide a reward for people who provide helpful/timely URLs [...]
As an example, suppose Alice is in the 99th percentile with respect to the tag "crypto" while Bob is in the 70th percentile with respect to that tag. In this case, Alice would have greater influence on the search ranking for "crypto" than Bob.
The overall ranking [of a user] is computed in terms of these tag-specific user percentiles: the score for a user is the sum of his/her percentiles with respect to all the tags associated with that user.
So it's clear that this isn't simply an estimation of a user's area of expertise, but of his area of expertise relative to all other users. Let's paraphrase their cryptic lingo.
How to Get a High CollaborativeRank Listing
- Be the first to bookmark a popular URL.
- The more people who bookmark this URL after you, the better.
- The tags you used for this URL are used to calculate your area of expertise.
It's clear that this system is easy to abuse when you want to improve your ranking.
Tips on improving your CollaborativeRank listing:
- Bookmark lots of URLs; at least some of them are going to be more popular than they were when you bookmarked them. (It's no coincidence that CollaborativeRank's top ranked users usually have way more than 2,000 bookmarks on del.icio.us, some have as much as 20,000.)
- Use tags that other people didn't think of using when they bookmarked the same URL. You'll be an expert on these topics in no time. (E.g., I use 'wifi' where other people use 'wireless', 'wlan', '802.11', etc).
- And most important of all, be quick. The sooner you bookmark a popular URL, the better.
Note that I did not actually try to test these hyoptheses though, so I could be wrong; a meaningful del.icio.us database is more important to me than an artificially high ranking.
Update: a couple of hours later I added links to my tags, and some additional explanations.