What is Active Learning and How Does it Work?

January 27, 2022

active learning

Active Learning is a machine learning (ML) technique where the algorithm can select data it wants to learn from. In active learning, the algorithm chooses which subset of examples to label next from the pool of previously unclassified data. Passive learning is different in that a user gives all known parameters as training labels without considering how useful this will be for future prediction.

The basic idea behind the active learner algorithm is that an ML algorithm may achieve a higher level of accuracy while working with a smaller number of training labels if given free rein to select the data it wishes to learn. The program may use this approach to query an authoritative source, such as a labelled dataset, in order to obtain the correct prediction for a certain problem.

The aim of this iterative learning technique is to speed up learning by minimizing the amount of time spent on data preparation and algorithm tuning. The trade-off is that an active learner algorithm typically takes more time to find the best training labels.

Active Learning Requirements

One of the most important considerations when using active learning is the quality of the data. To be effective, the data must be well-distributed across different classes so that the algorithm can identify relevant examples easily. If the data isn’t well-distributed, then it may be difficult for the algorithm to find good examples of each class, which could lead to poorer performance on later predictions.


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How Active Learning Works

Active learning works by giving the algorithm a starting point of labelled data. This forced choice is called an active instance, and the goal of the learner is to select as few as possible. The more it chooses, the higher its risk of mislabelling examples and deteriorating its performance on future predictions.

Active learning algorithms are better at learning from data sets with a lot of uncertainty. This is because they focus on instances that are most likely to lead to improved predictions. The four most common types of active learning algorithms are selective sampling, iterative refinement, uncertainty sampling, and query by committee. Each type has its own strengths and weaknesses:

  • Selective Sampling – The algorithm randomly selects a small number of instances from the data set and labels them. It then uses those instances to train the model.
  • Iterative-Refinement – The algorithm starts by selecting a random instance as the active instance. It then compares the prediction error on that instance to the prediction error on all of the other instances in the data set. If it finds a more accurate prediction on another instance, it reclassifies that instance as active and repeats the process.
  • Uncertainty Sampling – The algorithm randomly selects a small number of instances from the data set and labels them. It then uses those instances to train the model.
  • Query by Committee – The algorithm starts by selecting a random instance as the active instance. It then splits the data set into clusters, where each cluster contains similar instances. It then selects one active instance from each cluster.

Which Method is Best?

There’s no one-size-fits-all answer to this question. Different methods will work better for different models, and each method has its pros and cons. For example, uncertainty sampling works best when there are many examples that are all very similar to the instance you’re trying to classify. It doesn’t perform as well for models where some training instances contain more information than others (e.g., neural networks).

The Good and Bad of Active Learning

Active Learning performs best when it’s possible to find a good representative of the data set (i.e., one with a high margin or low complexity). It also scales well to large numbers of labelled instances while preserving computational resources by focusing on the most informative examples first. However, it requires some subject-matter knowledge about the task at hand in order to make an informed choice about which instance is best for labelling.

The idea behind Active Learning is to have the user chooses which instance to annotate, hence choosing the most informative.

First, let’s define what an active learner is – in the context of machine learning; it refers to a model that helps label AI training data by querying its owner. For example, if you are trying to build a spam detector, one approach would be to ask human users whether email messages are spam or not. If, however, you could ask only a subset of the users, this would be an active learning technique called “selective sampling”, since it selects instances based on their predicted usefulness for labelling.

One advantage of selective sampling over full coverage is that it can save time and cost while achieving the same or better accuracy. The main disadvantages are that it requires an oracle to tell the difference between important data and redundant data and that it is only applicable when there are enough labels to be had elsewhere.

Active Learning Use Cases

Active learning has found a number of applications in areas such as text categorization, document classification, and image recognition. It has also been used for cancer detection and drug discovery.

Text Categorization

One of the most common applications of active learning is text categorization, which is the task of assigning a category to a piece of text. In this application, the categories are usually a set of predefined labels such as “news”, “sports”, “entertainment”, and “opinion”. The goal is to automatically assign each piece of text to one of these categories.

Document Classification

Active learning can also be used for document classification, which is the task of automatically assigning a class to a document. In this application, the classes are usually a set of predefined labels such as “technical document”, “marketing document”, and “legal document”.

Image Recognition

Image recognition is another area where active learning can be used. In this example, we have an image and we’d like our annotators to label only relevant regions in the image. In other words, we need to make sure that each labelled region contributes maximum information for classifying the image. To achieve this objective, active learning will pick up the most interesting regions from unlabelled data and let them be processed by annotators.

This way, annotators don’t waste any time on labelling redundant parts of an image that would have remained untagged if they were just blindly assigning labels to all regions in an image.


Active Learning is a technique where the machine itself decides which are the most important data points to be labelled by a human. This has multiple benefits over traditional methods of Machine Learning. However, there’s still much research to be done in this area in order to determine which tasks and datasets are best suited for active learning approaches.

One question that remains unanswered is whether or not Active Learning always outperforms traditional methods – this is still an open question that requires further study. Additionally, it’s also not clear how well Active Learning scales with increasing data sizes. More work is needed in order to better understand the benefits and limitations of Active Learning approaches. Despite these uncertainties, Active Learning is a promising field that has already shown great potential for improving the accuracy of Machine Learning models.

Summary – Active Learning: Deep Learning is a type of Machine Learning that allows computers to learn on their own. Deep learning methods like Active Learning are typically used to solve very complicated problems with numerous variables. With active learning, the machine itself can determine which data points should be labelled, helping save time and effort.


Dieser Artikel wurde am 27.January 2022 von Clickblogger geschrieben.