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Anomaly vs. Outlier — What's the Difference?

By Urooj Arif & Maham Liaqat — Updated on April 20, 2024
Anomaly refers to something that deviates from what is standard, normal, or expected, often suggesting a glitch or inconsistency; outlier is a statistical term for a data point that differs significantly from other observations.
Anomaly vs. Outlier — What's the Difference?

Difference Between Anomaly and Outlier


Key Differences

An anomaly often implies a deviation from the norm that may indicate a problem or error, suggesting it interrupts the expected order or pattern. On the other hand, an outlier specifically refers to observations in a data set that are significantly different from the majority, and may not necessarily indicate an error but rather a natural variation within the data.
In general usage, anomaly is used more broadly across various contexts such as events, conditions, or phenomena that are unusual or unexpected. Whereas, outlier is predominantly used in statistical contexts or in discussions about data, focusing on its numerical distance from other data points.
Anomalies can suggest a qualitative deviation from what is typically observed or established, often sparking investigations or corrections in processes or systems. Outliers, however, might not always warrant such responses, as they can be an expected part of variability in statistical distributions.
In fields like astronomy, an anomaly might refer to irregularities in data or celestial phenomena that don’t fit theoretical models. Conversely, in statistics, an outlier is quantitatively assessed against a data set’s mean or median, identifying values on the extreme ends of the data spectrum.
While anomalies can often be seen as signs of errors, malfunctions, or peculiarities requiring further examination, outliers might be excluded from data analysis to better understand the typical trends and to avoid skewed interpretations.

Comparison Chart


Deviation from what is normal or expected
Data point that is distant from others

Context Usage

Broad (social, technical, natural)
Primarily statistical


Often suggests a problem or error
Natural variation or statistical exception


May prompt investigation or correction
Often excluded from analysis

Field Relevance

General, across various fields
Primarily in statistics and data analysis

Compare with Definitions


An irregularity in a typical pattern.
The anomaly in seismic data suggested an unrecorded earthquake.


An extreme deviation from the median or mean.
His test score was an outlier, much higher than the class average.


An oddity or peculiarity in behavior.
His sudden mood swing was an anomaly in his usual demeanor.


An exception not fitting the general pattern.
Her rapid recovery was an outlier in clinical trials.


A glitch or inconsistency within a system.
The software anomaly caused data loss.


A person or thing differing significantly from other members of a group.
As an outlier in his family of artists, he pursued a career in science.


An exception that challenges common rules.
The plant's growth in such arid conditions is an anomaly.


A value far removed from the main group of data.
The outlier in the dataset skewed the average income.


Something that deviates from the norm.
An unexpected dip in temperature was considered an anomaly.


A statistical anomaly often excluded from data analysis.
Outliers were removed to normalize the results.


Deviation or departure from the normal or common order, form, or rule.


In statistics, an outlier is a data point that differs significantly from other observations. An outlier may be due to variability in the measurement or it may indicate experimental error; the latter are sometimes excluded from the data set.


One that is peculiar, irregular, abnormal, or difficult to classify
"Both men are anomalies.


One that lives or is located outside or at the edge of a given area
Outliers of the forest standing in the field.


(Astronomy) The angular deviation, as observed from the sun, of a planet from its perihelion.


One that exists outside or at an extreme of a category, pattern, or expectation; an extreme case or exception
"those egg-laying outliers of mammaldom, the duck-billed platypus and the anteating echidna" (Natalie Angier).


A deviation from a rule or from what is regarded as normal; an outlier.


A value far from most others in a set of data
"Outliers make statistical analyses difficult" (Harvey Motulsky).


Something or someone that is strange or unusual.
He is an anomaly among his friends in that he's the only one who's unmarried.


A portion of stratified rock separated from a main formation by erosion.


(science) Any event or measurement that is out of the ordinary regardless of whether it is exceptional or not.
She disregarded some of the anomalies in the experiment, putting them down to miscalculation.


A person or thing situated away from the main body or outside its proper place.


(astronomy) Any of various angular distances.


An exception.


(biology) A defect or malformation.


(geology) A part of a formation separated from the rest of the formation by erosion.


(quantum physics) A failure of a classical symmetry due to quantum corrections.


(statistics) A value in a statistical sample which does not fit a pattern that describes most other data points; specifically, a value that lies 1.5 IQR beyond the upper or lower quartile.


(dated) An irregularity or disproportion.


One who does not live where his office, or business, or estate, is.


Deviation from the common rule; an irregularity; anything anomalous.
We are enabled to unite into a consistent whole the various anomalies and contending principles that are found in the minds and affairs of men.
As Professor Owen has remarked, there is no greater anomaly in nature than a bird that can not fly.


That which lies, or is, away from the main body.


The angular distance of a planet from its perihelion, as seen from the sun. This is the true anomaly. The eccentric anomaly is a corresponding angle at the center of the elliptic orbit of the planet. The mean anomaly is what the anomaly would be if the planet's angular motion were uniform.


A part of a rock or stratum lying without, or beyond, the main body, from which it has been separated by denudation.


Any deviation from the essential characteristics of a specific type.


A datum that lies significantly beyond the main cluster of data points on a graph or diagram; - suggestive of an error in measurement.


Deviation from the normal or common order or form or rule


A person who lives away from his place of work


A person who is unusual


An extreme deviation from the mean


(astronomy) position of a planet as defined by its angular distance from its perihelion (as observed from the sun)

Common Curiosities

How do researchers handle outliers in data analysis?

Researchers might exclude outliers to prevent them from skewing the results or analyze them separately to understand their causes.

Can an anomaly also be an outlier?

Yes, if the anomaly is in a data set and significantly different from other data points, it can also be considered an outlier.

What is the role of context in identifying an anomaly?

Context is crucial as it determines whether something deviates from what is expected within that specific situation or environment.

What methodologies are used to detect outliers in data?

Methods like statistical tests, visualizations, and automated algorithms are used to identify outliers in data sets.

What makes something an anomaly in general terms?

An anomaly is something unexpected or unusual that does not fit into the usual order or rules.

How can anomalies influence scientific research?

Anomalies can lead to new scientific discoveries or insights as researchers explore why the anomaly occurred.

Why is it important to detect anomalies?

Detecting anomalies is important to prevent potential problems, ensure quality control, and maintain system integrity.

Do anomalies always indicate a fault?

Not always; they might simply reflect unique or rare features in a system or environment, though they often prompt checks for faults.

What is the main difference between an anomaly and an outlier?

An anomaly is a deviation from the norm indicating a potential issue, whereas an outlier is a statistical term for data significantly different from other values.

Are outliers always errors or problems?

Not necessarily; outliers can simply represent natural variability within data and might not indicate an error.

Is an outlier always a negative indication in statistics?

No, outliers are not inherently negative; they can provide insights into the data set or indicate unique conditions or variations.

Can technological systems have outliers?

Technically, technological data can have outliers if the data points deviate significantly from others in measurements or performance metrics.

How do anomalies affect decision-making processes?

Anomalies can prompt further investigation, adjustments in strategies, or changes in operations to correct or understand the deviation.

Can an outlier be a positive feature in any scenario?

Yes, in scenarios like innovation or performance, outliers can indicate exceptionally good outcomes or capabilities.

What impact do outliers have on statistical analysis?

Outliers can greatly affect the mean, median, and other statistical measures, which can alter conclusions if not handled properly.

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Author Spotlight

Written by
Urooj Arif
Urooj is a skilled content writer at Ask Difference, known for her exceptional ability to simplify complex topics into engaging and informative content. With a passion for research and a flair for clear, concise writing, she consistently delivers articles that resonate with our diverse audience.
Co-written by
Maham Liaqat

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