Decision Trees in Machine Learning
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Questions and Answers

What is the main purpose of using entropy in classification trees?

  • To quantify missing information (correct)
  • To determine the speed of the classification
  • To simplify data representation
  • To increase the complexity of the data
  • What classification criterion is used in classification trees?

  • The shape of the objects only
  • Only the size of the objects
  • Only the color of the objects
  • Both shape and color of the objects (correct)
  • What does a good test in a classification tree indicate?

  • It is simple to answer
  • It leads to many conclusions
  • It requires more than two options
  • It carries much information about the class (correct)
  • What encoding is suggested for more frequent classes in information theory?

    <p>Using shorter encoding for frequent classes (B)</p> Signup and view all the answers

    Why might one stop splitting nodes in a decision tree?

    <p>When further classification does not yield additional information (C)</p> Signup and view all the answers

    What type of decision tree is used when Y is a nominal variable?

    <p>Classification tree (A)</p> Signup and view all the answers

    What is one of the main reasons for using decision trees over other models?

    <p>They are interpretable and can explain predictions. (C)</p> Signup and view all the answers

    In decision tree learning, what does the loss function ℓ signify?

    <p>The penalty for incorrect predictions. (C)</p> Signup and view all the answers

    What is the goal in the second learning task when using decision trees?

    <p>To minimize the risk of predictions on unseen data. (D)</p> Signup and view all the answers

    Why is learning decision trees considered NP-hard?

    <p>Finding the smallest tree consistent with data is complex. (A)</p> Signup and view all the answers

    What does recursive partitioning in decision trees involve?

    <p>Dividing data subsets until all subsets are completely pure. (B)</p> Signup and view all the answers

    What is the primary assumption made when learning decision trees from data?

    <p>Data contains examples of the output function. (D)</p> Signup and view all the answers

    What characterizes a regression tree in decision tree learning?

    <p>Y is numerical. (C)</p> Signup and view all the answers

    Which of the following is NOT a characteristic of decision trees?

    <p>They are always the most accurate predictive model. (B)</p> Signup and view all the answers

    What is often used to find a suitable decision tree when the risk cannot be computed?

    <p>Heuristics and approximations. (A)</p> Signup and view all the answers

    What is the primary purpose of a decision tree?

    <p>To represent a decision-making procedure (D)</p> Signup and view all the answers

    In a decision tree, what do the branches represent?

    <p>The tests or questions guiding the decision (C)</p> Signup and view all the answers

    What does the output attribute Y in a decision tree represent?

    <p>The target value assigned by the tree (D)</p> Signup and view all the answers

    How does a decision tree handle a continuous input attribute?

    <p>It forms ranges or intervals instead of individual values (C)</p> Signup and view all the answers

    Which of the following best describes the mapping function of a decision tree?

    <p>It maps input attributes to a unique output (B)</p> Signup and view all the answers

    What kind of functions can be represented by decision trees if the input attributes are boolean?

    <p>All possible boolean functions (A)</p> Signup and view all the answers

    Which of these examples does NOT represent a boolean function that can be depicted by a decision tree?

    <p>X1 + X2 (Arithmetic sum) (A)</p> Signup and view all the answers

    What role do the input attributes X1, X2, …, Xn play in a decision tree?

    <p>They define the input space and tested conditions (D)</p> Signup and view all the answers

    What does entropy measure in the context of a set of objects?

    <p>The amount of uncertainty regarding the class of an instance (C)</p> Signup and view all the answers

    In the equation for class entropy CE(S), what does pi represent?

    <p>The proportion of elements in S of class ci (B)</p> Signup and view all the answers

    What is the expected outcome when performing a question with high expected information gain?

    <p>Reduction of entropy (D)</p> Signup and view all the answers

    Given a set with classes A, B, and C, which scenario would result in the highest entropy?

    <p>Equal distribution of A, B, and C (B)</p> Signup and view all the answers

    What computation can be used to determine the information gain from a test in classification trees?

    <p>CE(S) - E[CE(Si)] (C)</p> Signup and view all the answers

    In the context of class entropy computation, what would be the effect of a class distribution with a high number of instances in one class?

    <p>Decrease in entropy (C)</p> Signup and view all the answers

    How is class entropy defined mathematically?

    <ul> <li>∑ pi log2(pi) (D)</li> </ul> Signup and view all the answers

    What is indicated by high entropy in a dataset?

    <p>Many possible outcomes, all equally likely (B)</p> Signup and view all the answers

    What is the relationship between entropy and information gain?

    <p>Information gain represents the reduction in entropy (C)</p> Signup and view all the answers

    What is the value of entropy when a set contains 15 instances of class A and 1 instance of class B?

    <p>0.34 (A)</p> Signup and view all the answers

    Flashcards

    What is a decision tree?

    A decision tree is a flowchart-like structure that visualizes a decision-making process by branching out based on various conditions (tests) to arrive at a final outcome (prediction).

    What are nodes in a decision tree?

    Each node in a decision tree corresponds to a test (question) that divides the data into different branches based on the answer. The tests are usually based on input attributes (features) of the data.

    What are leaf nodes in a decision tree?

    Leaf nodes represent the final decisions or predictions made based on the sequence of tests taken.

    How does a decision tree make a prediction?

    In a decision tree, each path from the root node to a leaf node represents a unique combination of test results, leading to a specific prediction.

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    How can a decision tree be represented as a function?

    The decision tree represents a function that maps input data to a specific output.

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    Can decision trees represent boolean functions?

    Boolean functions, expressed using true/false values, can be represented using decision trees.

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    How do decision trees handle continuous attributes?

    Decision trees can handle continuous attributes by splitting the data based on thresholds or ranges instead of individual values.

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    What can be done with decision trees?

    Decision trees are used in various machine learning tasks, such as classification and regression. They can be used to predict categorical outcomes or estimate numerical values.

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    Decision Tree

    A tree-like structure used in machine learning to make decisions by branching out based on tests performed on input data.

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    Decision Tree Node

    In a decision tree, each node represents a test performed on the input data, splitting the data into different branches based on the result of the test.

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    Decision Tree Leaf Node

    Leaf nodes in a decision tree represent the final prediction or classification made for a particular data instance, based on the sequence of tests taken from the root node to the leaf.

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    Classification tree

    A decision tree where the target variable (Y) is a category, like 'yes' or 'no'.

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    Choosing Tests in Decision Trees

    The process of choosing the best test to perform at each node in a decision tree, aiming to maximize the information gained about the target variable.

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    Entropy

    A measure used in information theory to quantify the uncertainty or information content of a random variable. In decision trees, entropy helps determine the best split based on information gain.

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    Regression tree

    A decision tree where the target variable (Y) is a number, like temperature or price.

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    Information Gain

    The gain in information achieved by performing a particular test in a decision tree node, measured by the reduction in entropy resulting from the split.

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    Learning decision trees

    The process of finding a decision tree that best fits the data, using a specific algorithm.

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    Information Gain as a Criterion

    Information gain is a criterion used to select the best test at each node in a decision tree. It prioritizes tests that result in the largest reduction in entropy, maximizing information about the target variable.

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    Smallest tree consistent with the data

    A decision tree that perfectly predicts all the data points in the training set.

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    Tree with minimal risk

    A decision tree that makes accurate predictions on new data, not just the training set.

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    Decision Trees with Continuous Attributes

    Decision trees can handle continuous attributes by splitting the data based on thresholds or ranges of values, instead of individual values as in discrete attributes.

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    Risk of a decision tree

    The expected value of how badly a decision tree performs on new data, calculated using a loss function.

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    Practical algorithms for learning decision trees

    Finding a decision tree that is small and accurate, using heuristics and only the training data.

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    Top-down induction of decision trees (TDIDT)

    The process of building a decision tree by starting with the full data set and repeatedly splitting it based on the best feature to predict the target variable.

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    Finding a test

    The process of finding the best feature to split the data in a decision tree.

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    Pure subset

    A subset of data that has a relatively homogeneous value for the target variable.

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    Class Entropy

    A measure of how uncertain we are about the class of an instance in a dataset.

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    Splitting in Decision Trees

    The process of choosing the best attribute or question to split the data at each node in a decision tree. The question that maximizes information gain is usually chosen.

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    Decision Trees: Handling Attribute Types

    The ability of a decision tree to represent both continuous (e.g., temperature) and discrete (e.g., color) attributes.

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    Decision Tree Evaluation

    The process of evaluating a decision tree's performance. Metrics like accuracy or error rate are used.

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    Decision Tree Pruning

    The process of simplifying a complex decision tree by removing redundant or unnecessary branches. It can improve the tree's readability and efficiency.

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    Regression with Decision Trees

    The process of predicting a numerical value based on input features using a decision tree.

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