# What is Precision and Recall

##### Precision and Recall in AI

Precision and recall are two key metrics used in the evaluation of classification models in artificial intelligence. These metrics are especially relevant when working with imbalanced datasets, where the number of examples from each class is different. Understanding precision and recall is essential for developing effective AI models and improving their accuracy.

Before diving into precision and recall, let’s start with some basic terms:

• True positive (TP): Correctly predicted data points that belong to the positive class.
• False positive (FP): Incorrectly predicted data points that do not belong to the positive class.
• True negative (TN): Correctly predicted data points that do not belong to the positive class.
• False negative (FN): Incorrectly predicted data points that belong to the positive class.
• Predicted positive (PP): The sum of the true positives and false positives.
• Actual positive (AP): The sum of the true positives and false negatives.

With these terms in mind, we can now define precision and recall:

• Precision: Precision is the fraction of correctly classified positive examples out of all predicted positive examples.
• Recall: Recall is the fraction of correctly classified positive examples out of all actual positive examples.

Mathematically, precision and recall can be expressed as:

• Precision = TP / PP
• Recall = TP / AP

It’s important to understand that precision and recall are inversely related. Increasing one will typically cause a decrease in the other. For example, a classifier that predicts all data points as positive will have high recall but low precision, while a classifier that only predicts highly confident data points as positive will have high precision but low recall.

So which metric is more important? It depends on the task at hand. In some scenarios, precision is more important, while in others, recall is more important. Here are a few examples:

• Fraud detection: In fraud detection, precision is typically more important than recall. It’s better to have a small number of false positives (i.e., flagging a legitimate transaction as fraudulent) than to have false negatives (i.e., missing a fraudulent transaction).
• Disease diagnosis: In medical diagnosis, recall is typically more important than precision. Missing a disease (false negative) can be life-threatening, while a false positive can lead to further testing or treatment.
• Information retrieval: In information retrieval, both precision and recall are important. Users expect to find all relevant documents (high recall) but also want to avoid irrelevant documents (high precision).

In practice, we often combine precision and recall into a single metric, such as F1-score or area under the precision-recall curve (AUPRC). The F1-score is the harmonic mean of precision and recall, defined as:

• F1-score = 2 * (precision * recall) / (precision + recall)

While the F1-score is a useful metric for comparing models, it can sometimes be misleading. For example, a model that achieves high recall but low precision may have a high F1-score, even though it’s not optimal for certain use cases. Therefore, it’s important to carefully consider the task at hand and choose the appropriate metric(s) for evaluating models.

Conclusion

Precision and recall are important metrics for evaluating classification models in AI. They measure a model’s ability to correctly classify positive examples and are especially relevant when working with imbalanced datasets. Understanding precision and recall is essential for developing effective AI models and improving their accuracy.