Doing Data Science

Chapter 11. Causality

Many of the models and examples in the book so far have been focused on the fundamental problem of prediction. We’ve discussed examples like in Chapter 8, where your goal was to build a model to predict whether or not a person would be likely to prefer a certain item—a movie or a book, for example. There may be thousands of features that go into the model, and you may use feature selection to narrow those down, but ultimately the model is getting optimized in order to get the highest accuracy. When one is optimizing for accuracy, one doesn’t necessarily worry about the meaning or interpretation of the features, and especially if there are thousands of features, it’s well-near impossible to interpret at all.

Additionally, you wouldn’t even want to make the statement that certain characteristics caused the person to buy the item. So, for example, your model for predicting or recommending a book on Amazon could include a feature “whether or not you’ve read Wes McKinney’s O’Reilly book Python for Data Analysis.” We wouldn’t say that reading his book caused you to read this book. It just might be a good predictor, which would have been discovered and come out as such in the process of optimizing for accuracy. We wish to emphasize here that it’s not simply the familiar correlation-causation trade-off you’ve perhaps had drilled into your head already, but rather that your intent when building such a model or system was not even to understand causality at all, but ...