Module - 5 Classification

Lesson - 8 Metrics for Classification Model

**Overview**

Classification metrics are a set of metrics used to evaluate the performance of classification models. These metrics are used to assess model accuracy, precision, recall, and other aspects. It is often used to compare different models or tune a single model for optimal performance. Classification metrics can be grouped into three main categories: Accuracy, sensitivity, specificity. Accuracy measures the overall performance of the model and is usually the most important metric. Sensitivity and specificity measure how well a model can distinguish different classes. Finally, other metrics such as AUC score, F1 score, and Kappa score measure model accuracy and recognition.

**General indicators:**

1.**Accuracy**: Accuracy of a classification model is the percentage of correctly classified instances out of all instances in the dataset. It can be expressed as a fraction or percentage and is calculated using the following formula:

```
Accuracy = (number of positives + number of positives/negatives) / total number of instances
```

**2. Precision:** Precision measures the proportion of true positives (correctly classified positive cases) out of all cases classified as positive. Calculated using the following formula:

```
precision= number of true positives / (number of true positives + number of false positives)
```

**3. Recall:** Recall measures the proportion of true positives among all actual positive instances. Calculated using the following formula:

```
recall = number of true positives / (number of true positives + number of false negatives)
```

4. **F1 score**: The F1 score combines precision and recall to produce a single score that is the harmonic average of the two metrics. Calculated using the following formula:

```
F1 score = 2 * (accuracy * memory) / (accuracy + memory)
```

5. **Receiver Operating Characteristic (ROC) Curve**: A ROC curve is a graphical representation of the trade-off between the true positive rate (recall rate) and the false positive rate (the percentage of negative instances falsely classified as positive) for different classification thresholds. Area under the ROC curve (AUC) is a metric that summarizes the ROC curve and produces a single value representing the overall performance of the model.

6. **Area under the ROC curve (AUC)**: Area under the ROC curve (AUC) is a metric that summarizes the ROC curve and produces a single value representing the overall performance of the model. Calculated using the following formula:

```
AUC = (true positive rate + false positive rate) / 2
```

7.**Confusion matrix:** A confusion matrix is a table that summarizes the classification results and indicates the number of true positive, true negative, false positive, and false negative results.

8.**Class Imbalance**: Class imbalance is a problem that occurs when one class (positive or negative) has significantly more instances than the other class. This can lead to a biased classification model targeting the majority class. Strategies to address class imbalance include data preprocessing techniques such as oversampling, undersampling, and SMOTE, as well as model-based approaches such as cost-sensitive learning and class-weighting algorithms.

9.**Precision recall curve**: Accuracy recall curve is another graphical representation of classification results and it is more informative than ROC curve in situations where data is not balanced. It shows precision and recall for different classification thresholds.

10.**Cross Validation**:

Cross-validation could be a strategy utilized to assess the execution of classification models and compare distinctive models. This includes part the dataset into k subsets, training a model on k-1 subsets, and testing on the remaining subsets.

Classification metrics are a set of measures utilized to assess the execution of a classification demonstrate. These measurements are utilized to evaluate the precision, accuracy, recall, and other perspectives of the model. They are frequently utilized to compare diverse models or to tune a single demonstrate for ideal execution. Classification measurements can be partitioned into three fundamental categories: accuracy, sensitivity and specificity. Accuracy measures the generally execution of the show and is as a rule the foremost imperative metric. Sensitivity and specificity measure how well the model can distinguish between different classes. Finally, other metrics such as the AUC score, F1 score, and Kappa score measure the precision and recall of the model.

**Common metrics:**

**Accuracy**:

The accuracy of a classification model is the proportion of correctly classified instances among all instances in the dataset.

It can be expressed as a fraction or percentage, and is calculated using the following equation:

```
Accuracy = (Number of True Positives + Number of True Negatives) / Total Number of Instances
```

**2. Precision**: Precision measures the proportion of true positives (correctly classified positive instances) among all instances classified as positive. It is calculated using the following equation:

```
Precision = Number of True Positives / (Number of True Positives + Number of False Positives)
```

**3. Recall**: Recall measures the proportion of true positives among all actual positive instances. It is calculated using the following equation:

```
Recall = Number of True Positives / (Number of True Positives + Number of False Negatives)
```

**4. F1 Score**: The F1 score combines precision and recall to give a single score that represents the harmonic mean of the two metrics. It is calculated using the following equation:

```
F1 Score = 2 * (Precision * Recall) / (Precision + Recall)
```

**5. Receiver Operating Characteristic (ROC) Curve**: A ROC curve is a graphical representation of the trade-off between true positive rate (recall) and false positive rate (the proportion of negative instances that are incorrectly classified as positive) for different classification thresholds. The area under the ROC curve (AUC) is a metric that summarizes the ROC curve, giving a single value that represents the overall performance of the model.

**6. Area Under the ROC Curve (AUC)**: The area under the ROC curve (AUC) is a metric that summarizes the ROC curve, giving a single value that represents the overall performance of the model. It is calculated using the following equation: AUC = (True Positive Rate + False Positive Rate) / 2

**7. Confusion Matrix:** A confusion matrix is a table that summarizes the classification results, showing the number of true positives, true negatives, false positives, and false negatives.

**8. Class Imbalance**: Class imbalance is a problem that arises when one class (positive or negative) has significantly more instances than the other class. This can lead to biased classification models that are skewed towards the majority class. Strategies for addressing class imbalance include data preprocessing techniques such as oversampling, undersampling, and SMOTE, as well as model-based approaches such as cost-sensitive learning and class-weighted algorithms.

**9. Precision-Recall Curve**: The precision-recall curve is another graphical representation of classification results, which can be more informative than the ROC curve in situations with imbalanced data. It plots precision against recall for different classification thresholds.

**10. Cross-validation**: Cross-validation is a technique used to evaluate the performance of a classification model and to compare different models. It involves partitioning the dataset into k subsets, training the model on k-1 subsets, and testing it on the remaining subset. This process is repeated for all k subsets, and the mean performance across all k runs is used as the performance metric for the model.

**Examples**

**Accuracy**For case, on the off chance that a classification demonstrate is trained on a dataset containing 100 occurrences, and it accurately classifies 80 of them, at that point the accuracy of the demonstrate is 80%.**Precision**: For illustration, in case a classification show is prepared on a dataset containing 100 occurrences, and it accurately classifies 80 of them as positive, but inaccurately classifies 10 of them as positive, at that point the accuracy of the show is 80%.**Recall**: For case, in case a classification show is trained on a dataset containing 100 occasions, and it accurately classifies 80 of them as positive, but misses 20 of the real positive occurrences, at that point the recall of the show is 80%.**F1 Score**: For illustration, in case a classification show contains a exactness of 70% and a review of 80%, at that point the F1 score of the demonstrate is 75%.**Receiver Operating Characteristic (ROC) Curve:**For case, a ROC curve of a classification demonstrate may appear that when the classification threshold is set to 50%, the genuine positive rate is 80% and the untrue positive rate is 20%.**Area Under Curve (AUC)**: For case, if the genuine positive rate of a classification demonstrate is 80% and the wrong positive rate is 20%, at that point the AUC of the show is 50%.**Confusion Matrix**: For illustration, a confusion matrix of a classification demonstrate may appear that it accurately classified 50 occurrences as positive and 50 occurrences as negative, but erroneously classified 10 occasions as positive and 10 occurrences as negative.**Class Imbalance**: For illustration, on the off chance that a dataset contains 100 positive occurrences and 1000 negative occasions, at that point this dataset is imbalanced.**Precision-Recall Curve**: For case, a precision-recall curve of a classification show may appear that when the classification limit is set to 50%, the accuracy is 70% and the review is 80%.**Cross-validation**: For illustration, to assess the performance of a classification demonstrate, the dataset can be divided into 5 subsets, and each subset can be utilized as the test set whereas the remaining 4 subsets are utilized to prepare the show. The mean performance over all 5 runs can at that point be utilized as the performance metric for the show.

**Conclusion**

Overall, metrics for classification models are important for assessing the performance of a model. They provide insight into the accuracy, precision, recall, and F1 score of a model, as well as the ROC curve and AUC score. These metrics help to compare the performance of different models and guide the selection of the best model. Additionally, they can be used to detect overfitting and guide the optimization of model parameters.

**Key takeaways**

- Accuracy: The accuracy metric measures the percentage of correctly classified instances. It is a good indicator of how well the model is performing, as it is easy to interpret and compare with other models.
- Precision: Precision measures the number of true positives divided by the number of true positives plus false positives. It is the ability of the model to correctly classify positive examples.
- Recall: Recall measures the number of true positives divided by the number of true positives plus false negatives. It is the ability of the model to identify all relevant instances.
- F1 Score: The F1 score is the harmonic mean of precision and recall, and it is a convenient metric for comparing different models.
- ROC Curve: The Receiver Operating Characteristic (ROC) curve plots the true positive rate (TPR) against the false positive rate (FPR). It is a good way to assess the performance of a model, especially for imbalanced datasets.
- AUC: The Area Under the Curve (AUC) is the area under the ROC curve. It is a measure of the model’s performance, and it can be used to compare different models.

**Quiz**

**1. Which of the following metrics can be used to measure the performance of a classification model?**

- AUC-ROC score
- F1 score
- Mean Squared Error
- Adjusted R Squared

**Answer**: A. AUC-ROC score, B. F1 score

**2.What does the Area Under the Curve (AUC) measure?**

- Model accuracy
- Model complexity
- Model performance
- Model precision

**Answer**: C. Model performance

**3.What is the purpose of the confusion matrix?**

- To determine model accuracy
- To measure the performance of the model
- To identify the correct and incorrect predictions made by the model
- To identify the most important features used by the model

**Answer**: C. To identify the correct and incorrect predictions made by the model

**4.What is the purpose of the precision and recall metric?**

- To measure the accuracy of the model
- To identify the correct and incorrect predictions made by the model
- To measure the performance of the model
- To identify the most important features used by the model

**Answer**: B. To identify the correct and incorrect predictions made by the model

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