How do you know if your model is going to work? Part 1: The problem

This month we have a guest post series from our dear friend and advisor, John Mount, on building reliable predictive models. We are honored to share his hard won learnings with the world.

Authors: John Mount (more articles) and Nina Zumel (more articles) of Win-Vector LLC.

“Essentially, all models are wrong, but some are useful.”
George Box

Here’s a caricature of a data science project: your company or client needs information (usually to make a decision). Your job is to build a model to predict that information. You fit a model, perhaps several, to available data and evaluate them to find the best. Then you cross your fingers that your chosen model doesn’t crash and burn in the real world.

We’ve discussed detecting if your data has a signal. Now: how do you know that your model is good? And how sure are you that it’s better than the models that you rejected?

Bartolomeu Velho 1568
Geocentric illustration Bartolomeu Velho, 1568 (Bibliothèque Nationale, Paris)


Notice the Sun in the 4th revolution about the earth. A very pretty, but not entirely reliable model.

In this latest “Statistics as it should be” series, we will systematically look at what to worry about and what to check. This is standard material, but presented in a “data science” oriented manner. Meaning we are going to consider scoring system utility in terms of service to a negotiable business goal (one of the many ways data science differs from pure machine learning).

To organize the ideas into digestible chunks, we are presenting this article as a four part series (to finished in the next 3 Tuesdays). This part (part 1) sets up the specific problem.

Read more.