Experimenter's bias

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See also: Machine learning terms

Experimenter's Bias in Machine Learning

Experimenter's bias, also known as researcher bias or confirmation bias, is a phenomenon that occurs when researchers unintentionally influence the outcomes of their studies or experiments to align with their expectations or preconceived beliefs. In the context of machine learning, experimenter's bias can manifest in various stages of the development process, including data collection, preprocessing, algorithm selection, and evaluation.

Data Collection and Preprocessing

During the data collection and preprocessing stages, experimenter's bias can lead to the introduction of systematic errors. This can occur when researchers inadvertently select or manipulate data in a way that reinforces their hypotheses or beliefs. For example, they may choose a dataset that is not representative of the population or sample, or they may apply preprocessing techniques that unintentionally distort the data in favor of a particular outcome.

Algorithm Selection and Parameter Tuning

Experimenter's bias can also affect the choice of machine learning algorithms and the process of parameter tuning. Researchers may be predisposed to select algorithms that they are more familiar with or that have performed well in previous experiments, even if these algorithms may not be the best fit for the current problem. Similarly, during the parameter tuning process, experimenters may subconsciously favor settings that are more likely to confirm their initial beliefs or expectations.

Model Evaluation

Finally, experimenter's bias can impact the evaluation of machine learning models. Researchers may consciously or unconsciously employ evaluation metrics or techniques that are more likely to produce favorable results for their models. This can lead to an overestimation of a model's performance and a lack of generalizability to real-world situations.

Mitigating Experimenter's Bias in Machine Learning

Several strategies can be employed to minimize the impact of experimenter's bias in machine learning research. These include:

Blind Analysis

Blind analysis is a technique in which researchers are unaware of the true values of the data or the expected outcomes of their models. This approach can help prevent researchers from making decisions based on their preconceptions or beliefs.


Cross-validation is a widely used technique in machine learning for assessing the performance of models. By splitting the dataset into multiple subsets and iteratively training and testing the model on different combinations of these subsets, researchers can obtain a more reliable and unbiased estimate of the model's performance.

Third-party Review

External review by independent researchers can help identify potential sources of experimenter's bias and ensure that the study's methodology and results are robust and reliable.

Explain Like I'm 5 (ELI5)

Experimenter's bias in machine learning is like a scientist who really wants their experiment to work, so they accidentally make choices that help the experiment succeed, even if it's not the best way to do it. This can happen when they pick the information they want to use, when they choose how their machine should learn, and when they check if the machine is doing a good job. To avoid this problem, scientists can use special ways to hide what they expect, test their machines more fairly, and ask other scientists to double-check their work.