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Overview

The first three questions of this homework is quite simple. We will use three different models to estimate the personalized treatment rule, and we will use the Sepsis dataset in all three questions. Keep in mind that the Sepsis dataset contains a BEST variable which is the doctor’s best guess for the treatment. And you should never use this variable in your model fitting. Only use it when evaluating the performance of your model. The data is provided on our course website.

Question 1: Direct Learning via Linear Model

Implement the direct learning approach with linear regression. Since this is an observational study, you should incorporate propensity score weighting when estimating the treatment rule. After obtaining the estimated treatment rule, compare it with the best label Sepsis$BEST and report your results.

Question 2: Outcome Weighted Learning

Use the outcome weighted learning via WeightSVM package with support vector machine to analyze the Sepsis dataset. You may have to consider the following decisions try some of them

If the performance is not as good as you want, try the DTRlearn2 package to perform this task again. Note that the DTRlearn2 package has already incorporated some rough internal tuning procedures and you only need to try different kernels. Report your results.

Question 3: Using the grf package

Use the grf package to find the optimal treatment rule for the Sepsis dataset. Compare the estimated treatment rule with the best label Sepsis$BEST and report your results. Furthermore, report the estimated average treatment effect (ATT) of this entire population (based on our understandings of the relationship between the conditional average treatment effect and the average treatment effect). You may also use the grf package documentation.

Question 4: Radon–Nikodym Theorem

Suppose that I want to estimate \(E(X^3)\) when \(X\) is a random variable from \(N(1,1)\). However, I do not know how to perform integration, and I could do is to generate random samples and perform numerical approximation. In addition, my machine can only generate random samples from \(N(2,2)\), but I do know the analytic density functions of both distributions. How can I estimate/approximate \(E(X^3)\) numerically using the Radon–Nikodym theorem? Use 5000 samples to make your estimation stable. Validate your answer using simulated data from \(N(1,1)\) or analytic integration.

Hint: if you ask GPT or write your prompt correctly with Copilot, it will give you the answer. But make sure to explain your procedure.