# Homework 5 DSCI 552 Decision Trees as Interpretable Models

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## Description

1. Decision Trees as Interpretable Models
ml/datasets/Acute+Inflammations.
(b) Build a decision tree on the whole data set and plot it.1
(c) Convert the decision rules into a set of IF-THEN rules.2
(d) Use cost-complexity pruning to find a minimal decision tree and a set of decision
rules with high interpretability.
2. The LASSO and Boosting for Regression
from https://archive.ics.uci.
edu/ml/datasets/Communities+and+Crime. Use the first 1495 rows of data as
the training set and the rest as the test set.
(b) The data set has missing values. Use a data imputation technique to deal with
the missing values in the data set. The data description mentions some features
are nonpredictive. Ignore those features.
(c) Plot a correlation matrix for the features in the data set.
(d) Calculate the Coefficient of Variation CV for each feature, where CV =
s
m
, in
which s is sample standard deviation and m is sample mean..
(e) Pick b

128c features with highest CV , and make scatter plots and box plots for
them. Can you draw conclusions about significance of those features, just by the
scatter plots?
(f) Fit a linear model using least squares to the training set and report the test error.
(g) Fit a ridge regression model on the training set, with λ chosen by cross-validation.
Report the test error obtained.
(h) Fit a LASSO model on the training set, with λ chosen by cross-validation. Report
the test error obtained, along with a list of the variables selected by the model.
Repeat with standardized4
features. Report the test error for both cases and
compare them.
(i) Fit a PCR model on the training set, with M (the number of principal components) chosen by cross-validation. Report the test error obtained.
1This data set is a multi-label data set. Sk-Learn seems to support building multi-label decision trees.
Alternatively, you can use the label powerset method to convert it to a multiclass data set. Also, you can
use the binary relevance method and build one decision tree for each label. It seems that the label powerset
approach is more relevant here. Is that right?
2You can use the code in
https://www.kdnuggets.com/2017/05/simplifying-decision-tree-interpretation-decision-rules-python.
html.
3Question you may encounter: I tried opening the dataset and download it but the file is not readable.
4
In this data set, features are already normalized.
1
Homework 5 DSCI 552, Instructor: Mohammad Reza Rajati
(j) In this section, we would like to fit a boosting tree to the data. As in classification
trees, one can use any type of regression at each node to build a multivariate
regression tree. Because the number of variables is large in this problem, one
can use L1-penalized regression at each node. Such a tree is called L1 penalized
gradient boosting tree. You can use XGBoost5
to fit the model tree. Determine
α (the regularization term) using cross-validation.
5Some hints on installing XGBoost on Windows: http://www.picnet.com.au/blogs/guido/2016/09/