CoolData blog

26 January 2012

More mistakes I’ve made

Filed under: Best practices, Peter Wylie, Pitfalls, Validation — Tags: , , , — kevinmacdonell @ 1:38 pm

A while back I wrote a couple of posts about mistakes I’ve made in data mining and predictive modelling. (See Four mistakes I have made and When your predictive model sucks.) Today I’m pleased to point out a brand new one.

The last days of work leading up to Christmas had me evaluating my new-donor acquisition models to see how well they’ve been working. Unfortunately, they were not working well. I had hoped — I had expected — to see newly-acquired donors clustered in the upper ranges of the decile scores I had created. Instead they were scattered all along the whole range. A solicitation conducted at random would have performed nearly as well.

Our mailing was restricted by score (roughly the top two deciles only), but our phone solicitation was more broad, so donors came from the whole range of deciles:

Very disappointing. To tell the truth, I had seen this before: A model that does well predicting overall participation, but which fails to identify which non-donors are most likely to convert. I am well past the point of being impressed by a model that tells me what everyone already knows, i.e. that loyal donors are most likely to give again. I want to have confidence that acquisition mail dollars are spent wisely.

So it was back to the drawing board. I considered whether my model was suffering from overfit, whether perhaps I had too many variables, too much random noise, multicolinearity. I studied and rejected one possibility after another. After so much effort, I came rather close to concluding that new-donor acquisition is not just difficult — it might be darn near impossible.

Dire possibility indeed. If you can’t predict conversion, then why bother with any of this?

It was during a phone conversation with Peter Wylie that things suddenly became clear. He asked me one question: How did I define my dependent variable? I checked, and found that my DV was named “Recent Donors.” That’s all it took to find where I had gone wrong.

As the name of the DV suggested, it turned out that the model was trained on a binary variable that flagged anyone who had made a gift in the past two years. The problem was that included everybody: long-time donors and newly-acquired donors alike. The model was highly influenced by the regular donors, and the new donors were lost in the shuffle.

It was a classic case of failing to properly define the question. If my goal was to identify the patterns and characteristics of newly-acquired donors, then I should have limited my DV strictly to non-donors who had recently converted to donors!

So I rebuilt the model, using the same data file and variables I had used to build the original model. This time, however, I pared the sample down to alumni who had never given a cent before fiscal 2009. They were the only alumni I needed to have scores for. Then I redefined my dependent variable so that non-donors who converted, i.e., who made a gift in either fiscal 2009 or 2010, were coded ‘1’, and all others were coded ‘0’. (I used two years of giving data instead of just one in order to have a little more data available for defining the DV.) Finally, I output a new set of decile scores from a binary logistic regression.

A test of the new scores showed that the new model was a vast improvement over the original. How did I test this? Recall that I reused the same data file from the original model. Therefore, it contained no giving data from the current fiscal year; the model was innocent of any knowledge of the future. Compare this breakdown of new donors with the one above:

Much better. Not fan-flippin-tastic, but better.

My error was a basic one — I’ve even cautioned about it in previous posts. Maybe I’m stupid, or maybe I’m just human. But like anyone who works with data, I can figure out when I’m wrong. That’s a huge advantage.

  • Be skeptical about the quality of your work.
  • Evaluate the results of your decisions.
  • Admit your mistakes.
  • Document your mistakes and learn from them.
  • Stay humble.

22 January 2010

Four mistakes I have made

Filed under: Pitfalls, skeptics — Tags: , , — kevinmacdonell @ 1:28 pm

Is your predictive model an Edsel? Build it right, then sell it right! (Photo by dok1 on Flickr, used via Creative Commons licence.)

There are technical errors, and then there are conceptual errors. I can’t identify all the technical issues you may encounter while data mining. But it’s useful to identify a few conceptual errors. These are mistakes that that may prove damaging to your efforts to win acceptance for your models and have them applied constructively in your organization. In this blog I always write about my own experience, so the examples of stupidity you’ll read about in today’s post are all mine.

Mistake No. 1: Using score sets to predict things they weren’t designed for.

When I began creating predictive scores, I frequently referred to them as “affinity” scores. That’s how I described them to colleagues, both to make the idea accessible and because I really believed that a high score indicated a high level of affinity with our institution. Then one day I tried to use the scores to predict which class years would be most likely to attend their Homecoming milestone reunion, and thereby predict whether attendance for the upcoming reunion year would go up or down. Based on the central tendency of the scores of each class, I predicted a drop in attendance. I circulated a paper explaining my prediction and felt rather brilliant. Fortunately, I was proven wrong. That year we set a new attendance record.

My dependent variable in these early models was Lifetime Giving; therefore, the model predicted propensity to give – nothing more, nothing less. If you want to predict event attendance, build an event-attendance model. If you want to gauge alumni affinity, build a survey, or participate in an alumni engagement benchmarking study. (In Canada, check out Engagement Analysis Inc.) Be cautious, too, about making bold predictions; why give skeptics more ammunition? If you want to feel brilliant, keep it to yourself!

Lesson: Don’t be too clever.

Mistake No. 2: Using a general model to predict a specific behaviour.

This is closely related to the first mistake. By ‘general model’ I mean one in which the dependent variable is simply Lifetime Giving. I call these models ‘general’ because they make no distinction among the various types of giving (annual, major, planned) nor among preferred channel (by mail, by phone, and for some, online). Building a general model is itself not a mistake: It will work quite well for segmenting your alumni for the Annual Fund, for example, and if this is your first model it might be best not to get too exotic with how you define your dependent variable (thereby introducing new forms of error).

Just be prepared to make refinements. Two years running, our calling program used a score set from a general model, which actually worked fairly well, except for one thing: A lot of top-scoring alumni were hanging up on our student callers. This phenomenon was very noticeable, and it was enough for some to say that the model was worthless. An analysis of hang-ups confirmed that the problem existed (yes, we track hang-ups in the database). But the analysis also showed that a lot of these hanger-uppers were good donors. The top scorers were very likely to give, but a lot of them didn’t care to receive a call from a student. (And for some reason had not already requested to be solicited by mail only.)

The fix was a new predictive model aimed specifically at the calling program, with a dependent variable composed solely of dollars received via telephone appeals. Fewer hang-ups, happier callers, happier donors.

Lesson: Know what you’re predicting.

Mistake No. 3: Assuming that people will ‘get it’.

If you were able to show your fundraising colleagues that high-scoring segments of the alumni population give a lot more than the others, and that low-scoring segments give little or nothing, you’d think your work was done. Alas, no. Don’t assume that you’ll simply be able to hand off the data, because if data mining is not yet part of your institution’s culture, it’s more than likely your findings will be under-used. You’ve got to sell it.

Ensure that your end-users know what to do with their scores. Be prepared to make suggestions for applications. (Is the goal cost-cutting through reducing the solicitation effort, or is it growth in number of donors, or is it pushing existing donors to higher levels of giving?) In fact, before you even begin you should have some sense of what would really be in demand at your institution, and then try to satisfy that demand. The Annual Fund is a good place to start, but you might find that there’s a more pressing need for prospect identification in Planned Giving.

At the other end, you’ll need to understand how your colleagues implemented their scores in order to do any follow-up analysis of the effectiveness of your model. For example, if you plan to analyze the results of the Annual Fund telephone campaign, you’ll need to know exactly who was called and who wasn’t, before you can compare scores against giving.

Lesson: Communicate.

Mistake No. 4: Showing people the mental sausage.

A few years ago I used to follow a great website called, created by Merlin Mann. His boss and friend said to him one day, “Y’know, Merlin, we’re really satisfied with the actual work you do, but is there any way you could do it without showing so much … I don’t know … mental sausage?”

Data mining and predictive modeling and cool data stuff are all exercises in discovery. When we discover something new, our natural urge is to share. In the past, I tended to share the wrong way: I would carefully reveal my discovery as if the process were unfolding in real time. These expositions (usually in the form of a Word document emailed around) would usually be rather long. The central message would often be buried in detail which someone not inhabiting my head would regard as extraneous.

Don’t expect people to follow your plot: They’re too busy. They need the back of a cereal box, and you’re sending them Proust. You need to make your point, back it up with the minimum amount of verbiage acceptable, incorporate visuals judiciously, and get the hell out.

Learn to use the charting options available in Excel or some other software to get your point across as effectively as possible. Offer to explain it face-to-face. Offer to present on it.

Lesson: Learn how to sell.

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