Table of Contents

## What is Chi Square in decision tree?

Chi-square is another method of splitting nodes in a decision tree for datasets having categorical target values. It can make two or more than two splits. It works on the statistical significance of differences between the parent node and child nodes.

**How do you prune a tree in decision tree?**

We can prune our decision tree by using information gain in both post-pruning and pre-pruning. In pre-pruning, we check whether information gain at a particular node is greater than minimum gain. In post-pruning, we prune the subtrees with the least information gain until we reach a desired number of leaves.

**What is the decision rule for Chi Square?**

Chi square value is NEVER negative. For df = 1 and alpha = . 05, the critical value is 3.84. So the decision rule is to reject ho if the Chi-Square test statistic is greater than 3.84, otherwise do not reject ho.

### What does pruning do in decision tree?

In machine learning and data mining, pruning is a technique associated with decision trees. Pruning reduces the size of decision trees by removing parts of the tree that do not provide power to classify instances.

**Can a decision tree have more than 2 splits?**

The decision tree will never create more splits than the number of levels in the Y variable.

**Which is better gini or entropy?**

The range of Entropy lies in between 0 to 1 and the range of Gini Impurity lies in between 0 to 0.5. Hence we can conclude that Gini Impurity is better as compared to entropy for selecting the best features.

#### Why tree pruning is useful in decision tree induction?

Tree pruning attempts to identify and remove such branches, with the goal of improving classification accuracy on unseen data. Decision trees can suffer from repetition and replication, making them overwhelming to interpret. In replication, duplicate subtrees exist within the tree.

**What are the advantages of post pruning over pre pruning?**

Advantages of Post-Pruning Post-pruning usually results in a better tree than pre-pruning because pre-pruning is greedy and may ignore splits that have subsequently important splits.

**How do you find the decision rule?**

The decision rule is: Reject H0 if Z > 1.645….Step 3.

- The decision rule depends on whether an upper-tailed, lower-tailed, or two-tailed test is proposed.
- The exact form of the test statistic is also important in determining the decision rule.
- The third factor is the level of significance.

## How do you conclude a chi-square test?

For a Chi-square test, a p-value that is less than or equal to your significance level indicates there is sufficient evidence to conclude that the observed distribution is not the same as the expected distribution. You can conclude that a relationship exists between the categorical variables.

**What is homogeneity in decision tree?**

Concept of Homogeneity: The decision tree checks whether H > some threshold then there is no further split. If the H < threshold then there will be further split. This process will be continued where the label is sufficiently homogeneous then a leaf is created.

**What is the main disadvantage of decision trees?**

Disadvantages of decision trees: They are unstable, meaning that a small change in the data can lead to a large change in the structure of the optimal decision tree. They are often relatively inaccurate. Many other predictors perform better with similar data.

### What are the two choices for pruning a decision tree?

Since each distinct path through the decision tree node produces a distinct rule, the pruning decision regarding that attribute test can be made differently for each path. In contrast, if the tree itself were pruned, the only two choices would be: Retain it in its original form.

**What are the effects of pruning a decision tree with minimum error?**

The tree is pruned back slightly further than the minimum error. Technically the pruning creates a decision tree with cross-validation error within 1 standard error of the minimum error. The smaller tree is more intelligible at the cost of a small increase in error. None.

**How can I reduce the running time of my decision tree?**

For a compromise between accuracy and an interpretable tree, try smallest tree pruning without early stopping. To produce an even smaller tree or reduce the running time while allowing accuracy to decrease, you can turn on early stopping. Use the template above to create and prune your own decision tree.

#### When to convert a decision tree to a set of rules?

P. Winston, 1992. Once a decision tree has been constructed, it is a simple matter to convert it into an equivalent set of rules. Converting a decision tree to rules before pruning has three main advantages: