PAKDD-10 Data Mining Competition Winner: Ensembles Again!

The PAKDD-10 Data Mining Competition results are in, and ensembles occupied the top 4 positions, and I think the top 5. The winner used Stochastic Gradient Boosting and Random Forests in Statistica, second place a combination of logistic regression and Stochastic Gradient Boosting (and Salford Systems CART for some feature extraction). Interestingly to me, the 5th place finisher used WEKA, an open source software tool.

The problem was credit risk with biased data for building the models, a good way to do the competition because this is the problem we usually face anyway: data was collected based on historic interactions with the company, biased by the approaches the company has used in the past rather than having a pure random sample to build models. Model performance was judged based on  Area under the Curve (AUC), with the KS distance as the tie breaker (it's not everyday I hear folks pull out the KS distance!).

One submission in particular commented on the difference between how algorithms build models and the metric used to evaluate them. CART uses the Gini Index, Logistic regression the log-odds, Neural Networks minimize mean squared error (usually), none of which directly maximize AUC. But this topic is worthy of another post.

The Trimmed Mean has Intuitive Appeal

I was listening to Colin Cowherd of ESPN radio this morning and he made a very interesting observation that we data miners know, or at least should know and make good use of. The context was evaluating teams and programs: are they dynasties or built off of one great player or coach. Lakers? dynasty. Celtics? dynasty. Bulls? without Jordan, they have been a mediocre franchise. The Lakers without Magic are still a dynasty. The Celtics without Bird are still a dynasty.

So his rule of thumb that he applied to college football programs was this: remove the best coach and the worst coach, and then assess the program. If they are still a great program, they are truly a dynasty.

This is the trimmed (truncated) mean idea that he was applying intuitively but is quite valuable in practice. When we assess customer lifetime value, if a small percentage of the customers generate 95% of the profits, examining those outliers or the long tail while valuable does not get at the general trend. When I was analyzing IRS corporate tax returns, the correlation between two line items (that I won't identify here!) was more than 90% over the 30K+ returns. But when we removed the largest 50 corporations, the correlation between these line items dropped to under 30%. Why? Because the tail drove the relationship; the overall trend didn't apply to the entire population. It is easy to be fooled by summary statistics for this reason: they assume characteristics about the data that may not be true.

This all gets back to nonlinearity in the data: if outliers behave differently than the general population, assess them based on the truncated populations. If outliers exist in your data, get the gist from the trimmed mean or median to reduce the bias from the outliers. We know this intuitively, but sometimes we forget to do it and make misleading inferences.

[UPDATE] I neglected to reference a former post that shows the problem of outliers in computing correlation coefficients: Beware of Outliers in Computing Correlations.

Upcoming DMRadio Interview: Analytics and Business Rules

On June 3rd, a week from this Thursday, I'll be participating in my third DMRadio interview, this time on business rules (the first two were related to text mining, including this one last year). I always have found these interviews enjoyable to do. I'll probably be discussing an inductive rule discovery process I participated in with a Fortune 500 company (and described at last February's Predictive Analytics World Conference in San Francisco).

Even if you can't be there "live", you can download the interview later.

Data Mining as a Top Career

More good news for data miners: http://www.signonsandiego.com/news/2010/may/19/hot-career-trends-for-college-grads-listed-in/

Data mining. The field involves extracting specific information or patterns from large databases. Career prospects are available in areas including advertising technology, scientific research and law enforcement.

I think they got it right: data mining (and it's siblings Predictive Analytics and Business Analytics) are growing in their appeal. But more importantly, I see organizations believing they can do it.

Of course time will tell. One sign will be how many more resumes (unsolicited) I get!

web analytics and predictive analytics: comments from emetrics

I just got back from the latest (and my first) eMetrics conference in San Jose, CA last week, and was very impressed by the practical nature of the conference. It was also a quite different experience for me to be in a setting where I knew very very few people there. I was there to co-present with Angel Morales "Behavioral Driven Marketing Attribution". Angel and I are co-founders of SmarterRemarketer, a new web analytics company, and this solution we described is just one nut we are trying to crack in the industry.

This post though is related to the overlap between web analytics and predictive analytics: very little right now. It really is a different world, and for many I spoke with, the mere mention of "predictive analytics" resulted in one of those unknowing looks back at me. In fairness, much that was spoken to me resulted in the same look!

One such topic was that of "use cases", a term used over and over in talks, but one that I don't encounter in the data mining world. We describe "case studies", but a "use case" is a smaller and more specific example of something interesting or unusual in how individuals or groups of individuals interact with web sites (I hope I got that right). The key though is that this is a thread of usage. In data mining, it is more typical that predictive models are built, and then to understand why the models are the way they are, one might trace through some of the more interesting branches of a tree or unusual variable combinations in something similar to this "use case" idea.

First, what to commend... The analyses I saw were quite good: customer segmentation, A/B testing, web page layout, some attribution, etc. There was a great keynote by Joe Megibow of Expedia describing how Expedia's entire web presence has changed in the past year. One of my favorite bloggers, Kevin Hillstrom of MineThatData fame gave a presentation praising the power of conditional probabilities (very nice!).  Lastly, there was one more keynote by someone I had never heard of (not to my credit), but is obviously a great communicator and is well-known in the web analytics world, Avinash Kaushik. One idea I liked very much from his keynote was the long tail: the tail of the distribution of keywords that navigates to his website contains many times more visits than his top 10. In the data mining world, of course, this would push us to characterize these sparsely populated items differently so they produce more influence in any predictive models. Lots to think about.

But I digress. The lack of data mining and predictive analytics at this conference begs (at least from me) the question: why not? They are swimming in data, have important business questions that need to be solved, and clearly not all of these are being solved well enough. That will be the subject of my next post.

Rexer Analytics Data Mining Survey

Calling all data miners! I encourage all to fill out the survey--it is the most complete survey of the data mining world that I am aware of. Use the link and code below, and stay tuned to see the results later in the year.

Survey Link:  www.RexerAnalytics.com/Data-Miner-Survey-2010-Intro2.html Access Code:  RS2458 The full description sent by Karl Rexer is below: Rexer Analytics, a data mining consulting firm, is conducting our fourth annual survey of the analytic behaviors, views and preferences of data mining professionals.  We would greatly appreciate it if you would: 1)       Participate in this survey, and 2)       Tell other data miners about the survey (forward this email to them). Thank you.  Forwarding the survey to others is invaluable for our “snowball sample methodology”.  It helps the survey reach a wide and diverse group of data miners.   Thank you also to everyone who participated in previous Data Miner Surveys, and especially to the people who provided suggestions for new questions and other survey modifications.  This year’s survey incorporates many ideas from survey participants. Your responses are completely confidential: no information you provide on the survey will be shared with anyone outside of Rexer Analytics.  All reporting of the survey findings will be done in the aggregate, and no findings will be written in such a way as to identify any of the participants.  This research is not being conducted for any third party, but is solely for the purpose of Rexer Analytics to disseminate the findings throughout the data mining community via publication, conference presentations, and personal contact.  If you would like a summary of last year’s or this year’s findings emailed to you, there will be a place at the end of the survey to leave your email address.  You can also email us directly (DataMinerSurvey@RexerAnalytics.com) if you have any questions about this research or to request research summaries. To participate, please click on the link below and enter the access code in the space provided.  The survey should take approximately 20 minutes to complete.  Anyone who has had this email forwarded to them should use the access code in the forwarded email. Survey Link:  www.RexerAnalytics.com/Data-Miner-Survey-2010-Intro2.html Access Code:  RS2458 Thank you for your time.  We hope the results from this survey provide useful information to the data mining community.

Predictive Analytics World Recap

Predictive Analytics World (PAW) just ended today, and here are a few thoughts on the conference.

PAW was a bigger conference than October's or last February's and it definitely felt bigger. It seemed to me that there was a larger international presence as well.

Major data mining software vendors included the ones you would expect (in alphabetical order to avoid any appearance of favoritism): Salford Systems, SAS, SPSS (an IBM company), Statsoft, and Tibco. Others who were there included Netezza (a new one for me--they have an innovative approach to data storage and retrieval), SAP, Florio (another new one for me--a drag-and-drop simulation tool) and REvolution.

One surprise to me was how many text mining case studies were presented. John Elder rightfully described text mining as "the wild west" of analytics in his talk and SAS introduced a new initiative in text analytics (including sentiment analysis, a topic that came up in several discussions I had with other attendees).

A second theme emphasized by Eric Siegel in the keynote and discussed in a technical manner by Day 2 Keynote Kim Larsen was uplift modeling, or as Larsen described it, Net Lift modeling. This approach makes so much sense, that one should consider not just responders, but should instead set up data to be able to identify those individuals that respond because of the marketing campaign and not bother those who would respond anyway. I'm interested in understanding the particular way that Larsen approaches Net Lift models with variable selection and a variant of Naive Bayes.

But for me, the key is setting up the data right and Larsen described the data particularly well. A good campaign will have a treatment set and a control set, where the treatment set gets the promotion or mailing, and the control set does not. There are several possible outcomes here. First, in the treatment set, there are those individuals who would have responded anyway, those who respond because of the campaign, and those who do not respond. For the control set, there are those who respond despite not receiving a mailing, and those who do not. The problem, of course, is that in the treatment set, you don't know which individuals would have responded if they had not been mailed, but you suspect that they look like those in the control set who responded.

A third area that struck me was that of big data. There was a session (that I missed, unfortunately) on in-dateabase vs. in-cloud computing (by Neil Raden of Hired Brains), and Robert Grossman's talk on building and maintaining 10K predictive models. This latter application was one that I believe will be the approach that we move toward as data size increases, where the multiple models are customized by geography, product, demographic group, etc.

I enjoyed the conference tremendously, including the conversations with attendees. One of note was the use of ensembles of clustering models that I hope will be presented at a future PAW.

Prinicpal Components for Modeling

Problem Statement

Analysts constructing predictive models frequently encounter the need to reduce the size of the available data, both in terms of variables and observations. One reason is that data sets are now available which are far too large to be modeled directly in their entirety using contemporary hardware and software. Another reason is that some data elements (variables) have an associated cost. For instance, medical tests bring an economic and sometimes human cost, so it would be ideal to minimize their use if possible. Another problem is overfitting: Many modeling algorithms will eagerly consume however much data they are fed, but increasing the size of this data will eventually produce models of increased complexity without a corresponding increase in quality. Model deployment and maintenance, too, may be encumbered by extra model inputs, in terms of both execution time and required data preparation and storage.

Naturally, the goal in data reduction is to decrease the size of needed data, while maintaining (as much as is possible) model performance, this process must be performed carefully.


A Solution: Principal Components

Selection of candidate predictor variables to retain (or to eliminate) is the most obvious way to reduce the size of the data. If model performance is not to suffer, though, then some effective measure of each variable's usefulness in the final model must be employed- which is complicated by the correlations among predictors. Several important procedures have been developed along these lines, such as forward selection, backward selection and stepwise selection.

Another possibility is principal components analysis ("PCA" to his friends), which is a procedure from multivariate statistics which yields a new set of variables (the same number as before), called the principal components. Conveniently, all of the principal components are simply linear functions of the original variables. As a side benefit, all of the principal components are completely uncorrelated. The technical details will not be presented here (see the reference, below), but suffice it to say that if 100 variables enter PCA, then 100 new variables (called the principal components come out. You are now wondering, perhaps, where the "data reduction" is? Simple: PCA constructs the new variables so that the first principal component exhibits the largest variance, the second principal component exhibits the second largest variance, and so on.

How well this works in practice depends completely on the data. In some cases, though, a large fraction of the total variance in the data can be compressed into a very small number of principal components. The data reduction comes when the analyst decides to retain only the first n principal components.

Note that PCA does not eliminate the need for the original variables: they are all still used in the calculation of the principal components, no matter how few of the principal components are retained. Also, statistical variance (which is what is concentrated by PCA) may not correspond perfectly to "predictive information", although it is often a reasonable approximation.


Last Words

Many statistical and data mining software packages will perform PCA, and it is not difficult to write one's own code. If you haven't tried this technique before, I recommend it: It is truly impressive to see PCA squeeze 90% of the variance in a large data set into a handful of variables.

Note: Related terms from the engineering world: eigenanalysis, eigenvector and eigenfunction.


Reference

For the down-and-dirty technical details of PCA (with enough information to allow you to program PCA), see:

Multivariate Statistical Methods: A Primer, by Manly (ISBN: 0-412-28620-3)

Note: The first edition is adequate for coding PCA, and is at present much cheaper than the second or third editions.

Predictive Analytics World - San Francisco

The next Predictive Analytics World is coming up next week. This is a conference look forward to very much because of the attendees; I have found that at the first two PAWs, there have a been a good mix of folks who are experts and those who are spinning up on Predictive Analytics. I'll be teaching a hands-on workshop Monday (using Enterprise Miner), and presenting a talk on using trees to generate business rules for a help-desk text analytics application on Tuesday the 16h. You can still get the 15% discount if you use the registration code DEANABBOTT010 in the registration process (this is not a sales plug--I won't receive any benefit from this). 


Look me up if you are going; I will be there both days (16th and 17th).

Is there anything new in Predictive Analytics?

Federal Computer Week's John Zyskowski posted an article on Jan 8, 2010 on Predictive Analytics entitled "Deja vu all over again: Predictive analytics look forward into the past". (kudos for the great Yogi Berra quote! But beware, as Berra stated himself, "I really didn't say everything I said")

Back to Predictive Analytics...Pieter Mimno is quoted as stating:

There's nothing new about this (Predictive Analytics). It's just old techniques that are being done better.

To support this argument, John quotes me related to work done at DFAS 10 years ago. Is this true? Is there nothing new in predictive analytics? If it isn't true, what is new?

I think what is new is not algorithms, but a better integration of data mining software in the business environment, primarily in two places: on the front end and on the back end. On the front end, data mining tools are better at connecting to databases now compared to 10 years ago, and provide the analyst better tools for assessing the data coming into the software. This has always been a big hurdle, and was the reason that at KDD 1999 in San Diego, the panel discussion on "Data Mining into Vertical Solutions" concluded that data mining functionality would be integrated into the database to a large degree. But while it hasn't happened quite the way it was envisioned 10 years ago, it is clearly much easier to do now.

On the back end, I believe the most significant step forward in data mining tools has been giving the analyst the ability to assess models in a manner consistent with the business objectives of the model. So rather than comparing models based on R^2 or overall classification accuracy, most tools give you the ability to generate an ROI chart, or a ROC curve, or build a custom model assessment engine based on rank-ordered model predictions. This means that when we convey what models are doing to decision makers, we can do so in the language they understanding and not force them to understand how good an R^2 of 0.4 really is. And then, data mining tools are to a greater degree producing scoring code that is usable outside of the tool itself by creating SQL code, SAS code, C or Java, or PMML. What I'm waiting for next is for vendors to provide PMML or other code for all the data prep one does in the tool prior to the model itself; typically, PMML code is generated only for the model itself.