What is Machine Learning?

Machine learning is currently one of the most popular data science and intelligent systems technologies, used widely in a variety of fields.

In this article we give you an in-depth exploration of Machine Learning, please use the links below to jump between sections.

Overview of Machine Learning

The term machine learning was coined in 1959 by Arthur Samuel, who defined it as giving computers the ability to learn without being explicitly programmed.

This is done by feeding the computer with data and allowing it to identify patterns in the data.

In other words, ML refers to the programming of computers in such a way that the computer is able to optimize its performance using example data or past experience.

It combines computation, algorithms, and statistical thinking, which together lead to data analysis, the construction of mathematical models, and reasoning based on observations automatically provided from the data.

Machine learning is not a new field, but it has seen a rapid increase in popularity in recent years. This is due to a number of factors, including the availability of large amounts of data, the development of powerful computing systems, and the increasing need for automated decision-making.

Why was machine learning introduced?

Machine learning was introduced to address the limitations of traditional programming.

Traditional programming requires writing precise instructions for the computer to follow, but this is not always possible for tasks where there is a limited understanding of the underlying problem.

For example, it is difficult to write an algorithm to convert human speech to text, or to identify spam emails because the data can be too complex or variable.

Machine learning algorithms, on the other hand, can learn from data to perform these tasks without explicit instructions. They can do this by identifying patterns in the data and using those patterns to make predictions.

Writing an algorithm in the traditional way was also practically impossible if the amount of data to be analyzed was too large or if it was very complex.

In addition to the challenges mentioned above, traditional programs were limited by their static nature, meaning that the program remains unchanged after it has been written and installed on the computer.

This is a problem in situations where the program should adapt to changes in the environment. For example, an email spam filter works poorly if it does not learn to identify new spam types.

In the situations mentioned above, machine learning (ML) can help.

Basic Idea behind Machine Learning

The basic idea behind machine learning involves programming a model that learns from data. In essence, it’s like giving a computer an algorithm that improves its efficiency, enabling it to perform tasks more quickly as it learns from the data it’s given.

Based on previously collected data and possible user activity, the aim is for the machine to learn from recurring situations better and better without being taught separately.

The goal is to find those features from context-related data, which, using various mathematical models and statistical methods, can determine the most likely outcome even from new, previously unseen data.

For example, a spam filter aims to identify and learn from emails those features that can be used to classify all future incoming messages as either spam or not spam.

The data that machine learning models are trained on can be of any type, including text, images, audio, and video. The quality and quantity of the data are essential to the success of a machine-learning model.

What is a Machine Learning Model?

A machine learning model is the output of a machine learning algorithm, consisting of the data used in the model and the algorithm used in the prediction.

A machine learning algorithm can be thought of as a similar algorithm to other algorithms used in programming, which can be described mathematically and in pseudocode. The algorithm is fitted to the training data, it processes the data, and it learns from it.

The model is created when the algorithm is applied to the training data. It contains the rules, constants, and structures produced by the algorithm from the data, which can be used to produce predictions from new data.

How does Machine Learning work?

Machine learning works by identifying patterns in data and using those patterns to make predictions.

ML has many applications, but the pre-processing steps before a machine learning application are more precisely defined and typically similar regardless of the application.

This is done in a series of steps:

1. Problem definition: The first step is to define the problem that you want to solve with machine learning. This includes identifying the types of input data and output data that you will need.
2. Data collection: Once you have defined the problem, you need to collect the data that you will use to train your machine learning model. This data can be collected from a variety of sources, such as databases, surveys, or sensors.
3. Data preprocessing: Once you have collected your data, you need to preprocess it to ensure that it is in the correct format and that it is free of errors. This may involve cleaning the data, removing outliers, and transforming the data into a format that your machine-learning algorithm can understand.
4. Model training: Once your data is preprocessed, you can train your machine learning model. This involves feeding the data to the algorithm and allowing it to learn the patterns in the data.
5. Model evaluation: Once your model is trained, you need to evaluate its performance on a held-out test set. This will help you to identify any potential problems with the model and to make necessary adjustments.
6. Model deployment: Once you are satisfied with the performance of your model, you can deploy it to production. This means making the model available to users so that they can use it to make predictions on new data.

This is a general overview of how machine learning works. The specific steps involved may vary depending on the type of machine learning algorithm that is being used and the problem that you are trying to solve.

Types of Machine Learning:

Machine learning methods can be broadly categorized into three groups: supervised learning, unsupervised learning, and reinforcement learning.

Supervised learning

Supervised learning is the most common type of ML, in which the learning algorithm is taught with data that includes both explanatory variables (features) and target variables (labels).

The algorithm’s goal is to produce a function that, based on the values of the explanatory variables, produces the value of the target variable as accurately as possible.

The target variable is the outcome that the machine learning model is intended to predict, such as a categorical classification of whether an email message is spam or not. The explanatory variables are features that affect the value of the target variable, such as features related to the sender, the sender, and the content of an email message, which can be used to classify the messages.

Unsupervised learning

Unsupervised learning is used when the computer is not given any labeled data. In unsupervised learning, the computer learns to identify patterns in the data without any prior knowledge.

For example, a computer could be given a set of images of various objects, and it would learn to group the images into categories based on their similarities.

Reinforcement learning

Reinforcement learning is a type of ML in which the computer learns to make decisions based on rewards and punishments. In reinforcement learning, the computer is given a set of rules and objectives, and it learns to make the best decisions to achieve those objectives.

For example, a robot could be taught to navigate a maze by rewarding it for taking the correct path and punishing it for taking the wrong path.

Semi-supervised learning

Semi-supervised learning is a type of ML that combines supervised and unsupervised learning. In semi-supervised learning, the computer is given a set of labeled data and a set of unlabeled data.

For instance, in the case of chatbots, machine learning can help them become more precise and reliable in understanding user inputs and providing relevant responses. Machine learning aids them in recognizing patterns and making predictions based on user input.

Types of Machine Learning Algorithms

Machine learning algorithms are used to find patterns in data and make predictions. There are many different types of machine learning algorithms, each with its own strengths and weaknesses. Here is a brief overview of some of the most common algorithms:

• Linear regression: Used to predict a continuous value, such as the price of a house or the number of customers who will visit a store on a given day.
• Logistic regression: Used to predict a binary outcome, such as whether someone will click on an ad or not.
• Decision trees: Used to classify data into different categories, such as whether an email is spam or not.
• Random forests: A more powerful version of decision trees that combines multiple trees to improve accuracy.
• Support vector machines: Used for both classification and regression, but can be complex and computationally expensive.
• K-nearest neighbors: A simple but effective algorithm that classifies data based on the most similar nearby data points.
• Naive Bayes: A probabilistic algorithm that is often used for text classification and spam filtering.
• Neural networks: Deep learning models that can be used for a wide range of tasks, such as image recognition and natural language processing.
• Clustering algorithms: Used to group similar data points together, such as grouping customers based on their purchase history.
• Principal component analysis: Used to reduce the dimensionality of data, which can make it easier to train and deploy machine learning models.
• Gradient boosting: A technique that combines multiple weak models to create a more powerful model.
• Recurrent neural networks: Neural networks that are designed to process sequential data, such as text or time series data.
• Long short-term memory: A type of recurrent neural network that is well-suited for handling long sequences.
• Convolutional neural networks: Deep learning models that are designed to process grid-like data, such as images and videos.

The difference between Machine Learning, AI and Deep Learning

Despite the strong connection, these three concepts should not be confused, as they differ from each other in terms of their goals and approaches.

• AI is a broad field that aims to create machines that can perform tasks that typically require human intelligence.
• ML is a subfield of AI that uses structured or semi-structured data to accomplish a predetermined task or to train machines to make predictions or decisions without being explicitly programmed.
• Deep learning is a subfield of ML that uses artificial neural networks to learn from data.

AI pioneer John McCarthy defined AI in 1955 as follows: “The goal of AI is to develop machines that behave as if they were intelligent.”

Unlike AI, ML does not seek to build an imitation of intelligent behavior, but rather to complement human intelligence, for example by performing tasks that humans cannot do.

Here is a table that summarizes the key differences between ML, AI, and deep learning:

Challenges in machine learning

Machine learning is a challenging field. There are many challenges that must be overcome in order to create effective machine learning algorithms.

• Overfitting: This occurs when the algorithm learns the training data too well and is unable to generalize to new data.

• Underfitting: This occurs when the algorithm does not learn the training data well enough and is unable to make accurate predictions.

• Data scarcity: Machine learning algorithms require a lot of data to train. If there is not enough data, the algorithm may not be able to learn the patterns in the data.
• Noisy data: Data can often be noisy, meaning that it contains errors or inconsistencies. This can make it difficult for the algorithm to learn the patterns in the data.

Factors Affecting Model Performance

1. Data Quantity and Quality

The effectiveness of machine learning models often depends on the data they are trained on and its quality. Poor-quality data leads to poor results. When it comes to data, both the amount and the quality matter.

Data Quantity: Having more data generally improves model performance, but there’s a limit to how much it helps. Beyond a certain point, adding more data doesn’t significantly boost performance, especially for certain deep learning methods.

Data Quality: Data quality is about how reliable the data is. It includes things like the accuracy of target values, errors in explanatory variables, missing data, and unusual data distributions. It’s crucial to select variables that have the most impact on the outcome.

Data Format: The way data is presented matters too. Algorithms work with numerical data, and the scale of variables affects how important they are in making predictions.

Data Distribution: If the data used for training is not representative of the overall population, the model may not make accurate predictions. This can lead to unfair decisions when machine learning is used in applications like hiring or lending decisions.

2. Hyperparameters

Hyperparameters in machine learning algorithms help control the complexity and performance of a model.

They are not the same as model parameters like weight values, which the algorithm adjusts while trying to build a function based on the data to predict target values.

By finding the optimal values for algorithm-specific hyperparameters, we can minimize prediction errors in the model. Hyperparameters are chosen and set before the algorithm runs, and they remain constant throughout the model’s training.

Examples of hyperparameters include the choice of optimization algorithm, the number of clusters, the selection of activation functions in neural networks, the number of hidden layers, the number of epochs, and the choice of error or loss functions.

The loss function is crucial for evaluating performance because it tells us how accurately the model’s predictions match the actual values. The ratio of data split between training and testing data is also considered a hyperparameter.

3. Overfitting and Underfitting

The generalization ability of a machine learning model is crucial for its performance. It indicates how well the model works with new, unseen data.

A machine learning model is essentially a mathematical model tailored to fit the data, describing it as accurately as possible.

Generalization becomes problematic when the model is either too simple or too complex. The terms bias and variance are associated with this trade-off.

Bias: Bias refers to a systematic measurement error, the difference between the average prediction error made by the model and the actual values. When bias is high, the model oversimplifies, leading to underfitting.

Variance: Variance measures the variability of the model’s predictions compared to the actual values. When predictions are close to actual values, variance is low. When predictions deviate significantly, variance is high, indicating overfitting.

Optimal Model: The ideal model finds a balance where bias and variance are both minimized.

Underfitting: Underfitting results in inaccurate outcomes for both training and test data. The model fails to discover correlations between explanatory variables and the target variable. This may happen due to insufficient training data or using a too simplistic model for complex data.

Overfitting: Overfitting produces precise results on training data but performs poorly on new, unseen data. This occurs when the training data does not represent the entire population, due to noise in the data, a small amount of training data, or an excessive number of explanatory variables.

Performance Metrics for Machine Learning Models

The evaluation of machine learning models depends on whether it’s a classification or regression task.

Classification Evaluation:

In classification tasks, accuracy is commonly used to assess a model’s performance. It measures how well the model can predict the correct class, separately for training and test data. The formula for accuracy is shown below:

Accuracy = Correctly predicted instances / Total instances

However, accuracy may not be suitable when the dataset has imbalanced class distribution, as it can lead to misleading results. In such cases, other metrics are needed.

Confusion Matrix:

To evaluate a classifier in binary classification, a confusion matrix is used. It divides cases into four categories: True Positive (correctly identified positive), False Negative (incorrectly identified negative), False Positive (incorrectly identified positive), and True Negative (correctly identified negative).

Precision and Recall:

Precision measures how many of the correctly predicted positive cases are actually positive, while recall measures how many of the actual positive cases are correctly identified. Both metrics should have higher values for better performance.

F1-Score:

To balance precision and recall, the F1-score is used. It is the harmonic mean of precision and recall and is especially useful when classes are imbalanced.

Receiver Operator Characteristics (ROC):

ROC curves visualize the trade-off between true positive rate and false positive rate for different thresholds. The area under the ROC curve (AUC) quantifies the overall performance of a classifier, with higher values indicating better performance.

Regression Evaluation:

In regression tasks, evaluating model performance is more straightforward. Good regression models produce predictions close to the actual values. Common metrics include Mean Squared Error (MSE) and Mean Absolute Error (MAE).

Mean Squared Error (MSE):

MSE measures the average of the squared differences between predicted and actual values. It highlights the impact of larger errors.

Mean Absolute Error (MAE):

MAE measures the average of the absolute differences between predicted and actual values. It provides insight into the overall accuracy of predictions.

If the metrics perform significantly worse on test data compared to training data, it suggests overfitting.

These metrics help in assessing the performance of machine learning models in different types of tasks.