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Bias Estimation in Machine Learning: Definition, Causes, and Mitigation Strategies

Bias is a common problem in data science, which can lead to inaccurate conclusions and unfair decisions. It can arise from various sources, such as ‌sampling methods, measurement errors, or model misspecification. Therefore, it is important to estimate the bias and account for it when making inferences or predictions from the data.

Bias Estimation in Machine Learning: Definition, Causes, and Mitigation Strategies

In this article, we will discuss the concept of bias estimation and various methods for estimating bias in machine learning. We will also explore the importance of bias estimation in ensuring fairness and equity in decision-making processes.

We will start by defining bias and its different types. Then, we will discuss some of the commonly used methods for bias estimation, like cross-validation. After that, we will investigate some of the methods used for bias reduction, like resampling methods and regularization techniques.

Next, we will explore ‌best practices in bias estimation in the fields of natural language processing and computer vision.

Finally, we will conclude by summarizing the key takeaways from the article and highlighting the importance of bias estimation in ensuring accurate and fair decision-making processes.

Bias in Machine Learning: Definition

Bias in machine learning refers to the systematic error or deviation in a model's predictions from the actual outcomes. In other words, it is a form of inaccuracy in a model that occurs when the model makes assumptions or generalizations based on limited or incomplete data. This can result in the model being skewed towards certain patterns or outcomes, leading to unfair or discriminatory results. Bias can arise from various sources, such as a skewed or imbalanced dataset, incomplete feature representation, or the use of biased algorithms. It is essential to identify and correct biases in machine learning models to ensure their accuracy and fairness in real-world applications before using them in decision-making positions.

Bias in Machine Learning: Why is it Dangerous?

Bias in machine learning can be dangerous because it can result in unfair or discriminatory outcomes that negatively impact certain groups or individuals. The following examples show how bias in machine learning can lead to unfair or discriminatory outcomes in different sectors:


A machine learning model trained on the resumes of successful employees at a company may be biased towards certain educational backgrounds or work experience, leading to discrimination against candidates from different backgrounds who may be equally qualified.

Criminal Justice

A machine learning model used to predict recidivism rates may be biased towards certain demographics or socioeconomic groups, leading to extended prison sentences or unfair treatment of certain groups.


A machine learning model used to diagnose diseases may be biased against certain health conditions, leading to misdiagnosis for certain groups.


A machine learning model used to target advertisements may be biased towards certain demographics or interests, perpetuating harmful stereotypes or excluding certain groups from marketing opportunities.

What is Bias Estimation?

As we understand the concept of bias and its dangers, let’s take a look at the bias estimation concept, which is a method of assessing and correcting inaccuracies in a machine learning model. It involves measuring the difference between the model's predicted outcomes and the actual outcomes to determine the extent of bias present in the model. 

The goal of bias estimation is to ensure that the model is fair and unbiased in its predictions. By identifying and correcting any bias, machine learning engineers can improve the accuracy and reliability of the model, making it more effective in real-world applications.

What is Variance?

To be able to understand how to calculate the bias, we also need to understand the variance. Variance refers to the sensitivity of a model to the fluctuations in the training data. When a model has high variance, it tends to fit too closely to the training data and may not generalize well to new data. This means that the model may perform well on the training data but poorly on the testing data. In simpler words, variance refers to the tendency of a model to overfit ‌training data, leading to poor performance on new, unseen data.

Bias-and-Variance Visualization

What is Irreducible Error?

As we understood the concepts of bias and variance, we can now take a look at a related concept which is the Irreducible Error. It is an error that cannot be reduced by improving the algorithm. It represents the amount of noise or variability in the data that cannot be explained by the model. This error is independent of the model's complexity and is inherent to the data. In contrast, bias and variance errors can be minimized by tuning the model. By reducing bias, we make the model more accurate on average, and by reducing variance, we make the model less sensitive to small fluctuations in the data.


How To Calculate An Estimate Of Bias?

Depending on the definitions of bias, variance, and irreducible error, we can move on to understand how to calculate the estimate of bias, which involves comparing the estimated value of a parameter to the true value of that parameter. Bias is the difference between these two values, and it can arise from various sources such as sampling methods, labeling errors, or model misspecification.

In this context, we can use the Empirical Risk Minimization (ERM) method, which compares the training error and test error to estimate the model's bias. If the training error is low and the test error is high, it suggests that the model is overfitting to the training data and has a high variance. In contrast, if both the training and test errors are high, it suggests that the model has a high bias and is underfitting the data. The difference between ‌training and test errors can provide an estimate of the model's bias.

More details about the bias estimation techniques will be discussed in the following paragraphs.


Why is Bias Estimation important?

Bias estimation is important in machine learning because it helps to identify and quantify any potential biases that may be present in a model's training data or algorithms. If these biases are left unaddressed, biases in machine learning models can result in unfair or inaccurate predictions and decisions, which can have serious consequences in real-world applications. 

By estimating and correcting for bias, machine learning engineers can help to ensure that their models are fair and accurate. This is especially important in sensitive areas such as healthcare, finance, and criminal justice, where biased algorithms can have a significant impact on people's lives. Additionally, addressing bias in machine learning can help to increase trust in the technology and reduce the risk of unintended harm.

Also, the estimation of bias can be useful in various applications such as statistical inference, where bias estimation can help to correct for bias and improve the accuracy of the estimates.

Common Sources of Bias in Machine Learning Models

Now, let’s deeply understand the main sources of bias. As we know, machine learning models are often trained on historical data that may contain biases and stereotypes, which can lead to biased predictions and decisions. The following are some common sources of bias in machine learning models:

Data Sampling Bias

The most general and common source of bias. It happens when the data used to train the model is not representative of the population it is intended to serve. For example, if a facial recognition model is trained on images of mostly white people, it may not perform well on images of people with darker skin tones. This can result in the model making more errors “biased” when attempting to recognize people of darker skin tones.

Labeling Bias

Sometimes even though the data represents the desired population well, the labels assigned to data samples are themselves biased. For example, if a model is trained to predict job performance based on resumes, but resumes from certain schools or neighborhoods are labeled as "low quality", the model may learn to discriminate against applicants from those schools or neighborhoods. This can result in unfair hiring practices and prevent talented individuals from getting the jobs they deserve.

Confirmation Bias

This occurs when the model is trained on data reinforcing existing beliefs or stereotypes. For example, if a model is trained to identify criminal behavior based on historical crime data, it may learn to associate certain races or ethnicities with criminality, even if there is no real causal link. This can lead to discriminatory practices by law enforcement agencies and the criminal justice system.

Prejudice Bias

This happens when the model reflects the prejudices of its creators. For example, if the development team is predominantly male, a model may learn to discriminate against women. This can result in biased decisions that negatively impact women and other marginalized groups.

Proxy Bias

This occurs when a model uses a proxy variable to make predictions that are indirectly biased. For example, if a model is used to predict creditworthiness based on income, it may indirectly discriminate against people with lower income levels who are more likely to be from marginalized communities. This can result in systemic discrimination against people who are already at a disadvantage.

Bias in machine learning models can have serious consequences, including perpetuating social inequalities, reinforcing stereotypes, and discriminating against certain groups. It is, therefore, essential to identify and correct for bias in machine learning models to ensure they are fair and unbiased. 

The Consequence of Biased Models in Real-World Applications

As we have seen in the examples in the previous section, the consequences of biased models in real-world applications can be severe and far-reaching. Biased models can perpetuate existing inequalities, reinforce stereotypes, discriminate against certain groups of people, and affect people’s lives in the real world.

In addition to perpetuating inequalities, biased models can also lead to reduced accuracy and reliability of predictions. If a model is biased, it may make inaccurate predictions for certain groups of people or fail to identify important patterns in the data. This can lead to missed opportunities, incorrect decisions, and negative consequences.

Furthermore, using biased models can also damage the reputation and trustworthiness of the organization or institution that uses them. This can lead to negative publicity, loss of business, and legal challenges.

In summary, biased models can have significant consequences in real-world applications. Therefore, it is crucial to identify and address bias in machine learning models to ensure fair and equitable outcomes. This accuracy can be achieved by understanding ‌common sources of bias, employing methods such as cross-validation to estimate the bias, and by using techniques like resampling and regularization to reduce it. So, let’s take a look at the most popular bias estimation techniques.

Cross-Validation: A Powerful Technique for Bias Estimation

Cross-validation is an essential technique for estimating bias in machine learning models, particularly in cases where the dataset is limited or imbalanced. Cross-validation is a resampling method that involves partitioning the dataset into multiple subsets, or folds, and using each fold in turn as a validation set to evaluate the model's performance. By repeating this process multiple times, cross-validation estimates the model's performance on unseen data, which can be used to detect and correct bias.

One common type of cross-validation is k-fold cross-validation, which involves dividing the dataset into k equally sized folds and using each fold as the validation set while training the model on the remaining k-1 folds. This technique is particularly useful when the dataset is small or imbalanced, as it allows the model to be trained on as much data as possible while still providing an estimate of its generalization performance. 

Another type of cross-validation is leave-one-out cross-validation, which involves leaving out one sample at a time as the validation set and training the model on the remaining samples. This technique can be computationally expensive, but it provides a more accurate estimate of the model's performance than k-fold cross-validation, particularly when the dataset is very small.

Cross-validation can help identify bias in machine learning models by estimating the model's generalization performance, which is its ability to perform well on new, unseen data. If the model performs well on the training data but poorly on the validation data, this may indicate that the model is overfitting to the training data and may not generalize well to new data. 

On the other hand, if the model performs poorly on both the training and validation data, this may indicate that the model is underfitting and may not capture the underlying patterns in the data. By using cross-validation to estimate bias, machine learning engineers can fine-tune their models and ensure that they are robust and reliable in real-world applications. Overall, cross-validation is a powerful tool for bias estimation in machine learning and should be standard practice for all machine learning engineers.


Bootstrapping: An Effective Approach to Bias Estimation

Bootstrapping is another common approach in the field of bias estimation. It is a resampling technique used to improve the accuracy and robustness of the estimation process. It involves repeatedly sampling data from a dataset with a replacement and estimating the bias using each sample. By doing so, it creates multiple subsets of the data, each with different combinations of observations, and it allows us to estimate the variability of the bias estimates across these different samples.

In bootstrapping, the original dataset is treated as the population, and new datasets are generated by random sampling with a replacement from this population. The size of the new datasets is typically the same as the size of the original dataset. The process of bootstrapping involves repeating the sampling process multiple times, each time generating a new dataset and each time estimating the bias on this new dataset.

The bias estimates obtained from each iteration of bootstrapping are then used to compute the mean and variance of the estimates. This provides a more accurate and robust estimate of the bias than a single estimate obtained from a single dataset. Bootstrapping is particularly useful when the dataset is small or when the bias estimation method is sensitive to the choice of data samples.

However, it is important to note that bootstrapping may be computationally expensive and requires careful consideration of subset size and parameter tuning to ensure accurate bias estimates.


Regularization Techniques: A Robust Method for Reducing Bias

Another popular technique utilized in the domain of bias estimation is regularization. Regularization involves adding a penalty term to the objective function of a model, which helps to prevent overfitting and improve generalization performance. The penalty term can take different forms, such as L1, L2, or elastic net regularization, and its strength is controlled by a hyperparameter that needs to be tuned.

Regularization effectively reduces bias and variance in machine learning models because it helps to balance the trade-off between fitting the training data too closely and capturing the underlying patterns in the data. Although regularization is more effective in mitigating the issue of overfitting and reducing the variance of a model, it can also lead to a decrease in bias. By penalizing the complexity of the model, regularization encourages simpler and more interpretable models that are less likely to overfit noise or irrelevant features.

Regularization techniques are widely used in various machine learning domains, such as regression, classification, and deep learning. For example, L1 regularization is commonly used in sparse feature selection and can help identify the most important features in a model, while L2 regularization is useful for reducing the impact of outliers and improving the stability of the model.

To sum up, the main purpose of regularization is to decrease variance in machine learning models. However, it may also have an effect on reducing bias. By decreasing overfitting and enhancing the general performance of the model, regularization can enhance the accuracy and reliability of the results generated by the model.

Comparing Techniques for Bias Estimation in Machine Learning

Comparing techniques for bias estimation in machine learning is crucial for selecting the most appropriate method for a given dataset and model. As we discussed in the previous sections, there are several techniques available for bias estimation; each technique has its strengths and weaknesses. 

The choice of method depends on factors such as the size and complexity of the dataset, the type of model being used, and the goals of the analysis. To compare techniques, researchers often use metrics such as precision, recall, and F1 score, among others. Additionally, they may also consider factors such as computational efficiency, ease of implementation, and interpretability.  Therefore, there is no global best choice.

Ultimately, the most effective technique for bias estimation will depend on the specific context and goals of the analysis. Therefore, it is important to carefully evaluate and compare different techniques to ensure the most accurate, robust, and unbiased model possible.

Best Practices For Bias Correction In Image Processing

Computer vision is an area of artificial intelligence that focuses on training machines to see and understand images and videos. To ensure that computer vision models are fair and accurate, it is important to address potential sources of bias. There are several best practices that can be followed to address bias in computer vision.

  • First, it is essential to have a diverse and representative dataset. This means collecting data from various sources and ensuring that the data is balanced regarding gender, race, and other important factors in the specific task. This can help prevent the model from learning biases that may be present in the data.

  • Second, it is important to select features and preprocessing techniques carefully. Some preprocessing techniques can introduce biases into the model, so it is important to carefully evaluate and test these techniques to ensure that they do not affect the model's accuracy.

  • Third, it is essential to use appropriate evaluation metrics to assess the model's performance. This includes metrics such as precision, recall, and F1 score, which can help identify biases in the model's predictions.

  • Finally, it is important to continue monitoring the model's performance and making updates as needed. This can include retraining the model on new data, adjusting the features and preprocessing techniques used, or even completely redesigning the model if biases persist.

By following these best practices, it is possible to address bias in computer vision and develop accurate and reliable machine-learning models that can be used in the real world.

Best practices for bias correction in NLP

Natural Language Processing (NLP) is a subfield of computer science and artificial intelligence that focuses on enabling computers to understand and interpret human language. It involves teaching machines to process and analyze large amounts of natural language data, such as speech and text, to extract meaning and patterns from them. Bias in NLP models can cause unfair or inaccurate predictions, leading to real-world consequences such as discrimination or misinformation. Therefore, it is crucial to correct the bias in NLP models. 

  • First, one common source of bias in NLP is the over-representation or under-representation of certain groups in ‌training data. To address this, best practices for bias correction in NLP involve using techniques such as data augmentation, where additional examples are generated from existing data to increase the diversity of the training data.

  • Second, debiasing algorithms such as adversarial training can be used to mitigate the impact of biased data, where a separate model is trained to identify and correct bias in the primary model, and counterfactual data augmentation, which involves generating hypothetical data that changes the sensitive attributes of an example to reduce bias. 

  • Third, like in ‌computer vision, it is important to ensure that the evaluation metrics used to assess NLP models do not inadvertently perpetuate bias, such as by giving higher weight to certain groups or data types. To achieve this, best practices recommend using evaluation metrics that are sensitive to both accuracy and fairness, such as equalized odds or demographic parity. 

Overall, bias correction in NLP requires a combination of careful attention to training data, the use of appropriate techniques to mitigate bias, and the selection of fair evaluation metrics. So, it is essential to involve a diverse team of experts in the development and training of NLP models. This can help to identify any biases or assumptions that may be present in the model and ensure that the model is representative of a broad range of perspectives and experiences.

Future Research Directions in Bias Estimation in Machine Learning

As machine learning continues to grow in importance and influence in various fields, it is clear that there is a need for continued research and development in bias estimation. One area of focus for future research is the development of more robust and efficient techniques for identifying and correcting bias in the data.

Another important direction is exploring the impact of different types of bias on machine learning models, including intersectional and structural biases. Additionally, more research is needed to understand better the social and ethical implications of bias in machine learning and to develop strategies for mitigating these effects. 

Finally, there is a need for greater diversity and inclusion in the development and evaluation of machine learning models to ensure that they are equitable and representative of diverse perspectives. By pursuing these research directions, we can work towards developing more accurate, fair, and ethical machine learning models that benefit society as a whole with full fairness.

Why Bias Estimation is Critical for Responsible and Ethical AI

Bias estimation is critical for responsible and ethical AI because machine learning models are increasingly used to make important decisions that have a significant impact on people's lives, such as hiring decisions, loan approvals, and medical diagnoses. If these models are biased, they can lead to unfair and discriminatory outcomes, perpetuate existing inequalities, and harm marginalized communities. Therefore, it is essential to employ bias estimation techniques to identify and correct for potential biases in the data and the model. Moreover, responsible and ethical AI requires a commitment to diversity and inclusion, transparency, and ongoing monitoring and evaluation of the model's performance to ensure that it remains unbiased and accurate. By prioritizing bias estimation and correction, we can build machine learning models that are not only technically sound but also equitable, ethical, and socially responsible.

Bias Estimation: Final Thoughts

In conclusion, bias estimation is a critical aspect of responsible and ethical AI. Machine learning models are susceptible to various sources of bias, such as data bias, algorithmic bias, and cognitive bias. To address these issues, various techniques can be used, including cross-validation, bootstrapping, and regularization. These techniques help to estimate and correct bias in machine learning models. 

While bias estimation is not a foolproof method, it can help reduce the negative impact of bias in AI applications. It is essential to understand the sources of bias and to use the appropriate bias estimation techniques to ensure that AI models are fair and equitable. By continuing to research and develop new techniques, we can work towards a future where AI is free from bias and promotes inclusivity and diversity.


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