Wednesday, May 02, 2007

Explicit vs. implicit data for news personalization

A paper at the upcoming WWW 2007 conference, "Open User Profiles for Adaptive News Systems: Help or Harm?" (PDF), concludes that allowing users to edit profiles used for news personalization can result in worse personalization.

From the paper:
Despite our expectations, our study didn't confirm that the ability to view and edit user profiles of interest in a personalized news system is beneficial to the user. On the contrary, it demonstrated that this ability has to be used with caution.

Our data demonstrated that all objective performance parameters are lower on average for the experimental system. It includes system recommendation performance as well as precision and recall of information collected in the user reports.

Moreover, we found a negative correlation between the system performance for an individual user and the amount of user model changes done by this user. While the performance data vary between users and topics, the general trend is clear – the more changes are done, the larger harm is done to the system recommendation performance.

The results of our study confirmed the controversial results of Waern's study: the ability to change established user profiles typically harms system and user performance.
The paper was not clear on exactly why editing the profiles made the personalization worse, but I would look to what Jason Fry at the Wall Street Journal wrote several months back:
When it comes to describing us as customers and consumers, recommendation engines may do the job better than we would.

In other words, we lie -- and never more effectively than when we're lying to ourselves ... I fancy myself a reader of contemporary literature and history books, but I mostly buy "Star Wars" novels and "Curious George" books for my kid.
As I wrote after seeing Jason's article, "Implicit data like purchases may be noisy, but it also can be more accurate. You may say you want to watch academy award winners, but you really want to watch South Park. You may say you want to read Hemingway, but you really want to read User Friendly."

See also an April 2004 post where I said, "When you rely on people to tell you want their interests are, they (1) usually won't bother, (2) if they do bother, they often provide partial information or even lie, and (3) even if they bother, tell the truth, and provide complete information, they usually fail to update their information over time."


Anonymous said...

Ok, so manipulating keywords is not the best approach for news recommendation. But I do find one of the other studies that the authors cite quite interesting:

"Koenemann and Belkin [15] on different levels of the user’s control on the expansion terms show that the increasing openness of the expansion terms and the higher level of the user’s control on the query expansion improve search effectiveness. This includes the findings that 1) participants performed 15% better when they were able to view and manipulate the terms, 2) they used less iterations to develop equally good or better queries [snip]"

So while word-level manipulation is not good for recommendation, it is good for ad hoc (web style) search. In the latter task, not only is precision improved, but fewer iterations are required.

In other words, users are lazy, and allowing them to directly manipulate explicit ad hoc search data cuts down the total amount of work that they have to do! And yet I constantly hear from you, from Danny Sullivan, from Google, that users are unwilling to do this type of explicit work, even if it means less overall work, total. Users, paradoxically, would rather take the long route, and type in more queries, over and over.

I think this recommendation paper you cite suffers from a similar paradox. With adhoc search users can get better results with less total work by manipulating explicit data, but they do NOT like to do it. With recommendation, users actually get worse results with more total work by manipulating explicit data, but users actually DO like to do it.

Do you see these eerie reverse parallels? Any thoughts on the origin or nature of these paradoxes?

Greg Linden said...

Hi, Jeremy. You make good points as always.

However, I think you might be making a leap from seeing less iterations with searching with a different interface to finding a reduction in the total amount of work.

Not only does a more complicated interface take time to learn and understand, but it may take more time per search to formulate a good query. It easily could be more iterations with less work per iteration versus fewer iterations with more work on each iteration.

I think an example of this is advanced search syntax, which is rarely used, but does allow more complicated queries. Why is it rarely used? Because it is faster to iterate with a simple interface.

I think the seeming paradox in the recommendations paper can be resolved in a similar way. Users like the feeling of being in control, but they turn out to often have a hard time using that control to get what they want.

Mike Dierken said...

Thanks for the link to that paper. We have already taken the position that implicit information may be more useful than explicit and we are busily working on the gathering, summarizing and utilizing of tons of implicit information about our members.
That being said, we could also use some expertise in this area so if you know of someone who may be a good fit, please have them contact me.

Anonymous said...

Greg, how right of you to call me out if I am making too big of a leap, there. But I'm not (or the K&B paper is not) talking about any sort of advanced query syntax. The K&B paper is very similar to this WWW'07 paper; it is about showing the user the dozen terms that it system would automatically add to the query, and giving the user the power to veto or add to that list. "Add or remove" a word is hardly advanced query syntax, and hardly takes training to understand. It is just taking implicitly added data, and making it explicit and manipulatable by the user.

So again, given that both papers seem to be doing something very similar, i.e. "explicitizing" a dozen or so automatically-generated query terms and letting the user manipulate those terms, why does the nature ("pull" versus "push") of the information gathering have such an impact on the effectiveness of the explicitization? (Ad hoc search is "pull", recommendation is "push".) Explicitization seems to work for "pull", but not work for "push". Why?

Anonymous said...

I think the seeming paradox in the recommendations paper can be resolved in a similar way. Users like the feeling of being in control, but they turn out to often have a hard time using that control to get what they want.

Apologies for being dense, but I still do not see how this resolves the seeming paradox in the recommendations paper. Users are lazy, right? But when it comes to the recommendations ("push") arena, their desire for control overrides their laziness, so that they actually prefer the explicitization, even if they suck at using it. At the same time, when it comes to the ad hoc search ("pull") arena, users' desire for control does not override their laziness. Users end up not wanting to give "add/remove term" feedback. Even though the experiments show that they would get better results if they did.

So this is what is confusing me. Here you have the same sort of explicitization being done, essentially the same type of data, with the same type of "add/remove term" user interface. And in one case, desire for control overrides laziness, and in the other laziness overrides desire for control. And again, the only real difference between the two cases is that one is "push" and the other is "pull". What gives, here?

Anonymous said...


Since you are discussing www2007, did you catch the Google paper "Google News Personalization: Scalable Online Collaborative Filtering". It gives some explicit details on using mapreduce for large scale EM algorithm implementations and collaborative filtering. Any thoughts on the approach they describe?


Greg Linden said...

Thanks, Peter, I was reading that paper a few days ago.

It is a remarkable piece of work -- an impressive and even intimidating example of what Google can do with its cluster and data -- but not without at least some flaws.

I have an analysis of the paper drafted, but have not had a chance to convert the notes into a post. As I am sure you can guess, that takes a fair amount of time, and, unfortunately, I am traveling right now. I hope to have something up next week.