Understanding outliers: What They are and Why They Matter
Tags: python, machinelearning, discuss, learning
Published: 2024-06-28 21:47:14

**Outlier** is a term often used in statistical analysis.
It is a data point that significantly differs from the rest of the data in a dataset.

Imagine a group of students taking a test where most scores fall within the range of 60-70, but one student scores 30 and another scores 90. These two extreme scores are illustrations of outliers.

In this blog post , we'll explore what outliers are and their importance.

## Understanding outliers

Outliers are data points that fall far outside the normal expected range of values in a dataset.
They can occur due to various reasons, such as measurement errors, natural variability, or unique circumstances.
Outliers can lead to skewness in statistical analysis which then leads to inaccurate results and conclusions if not addressed appropriately.

![Outlier](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/1ividtnemsxlccjwxk24.png)


## Types of outliers

1. **Global outliers**
These are data points that are significantly different from majority of the data in the dataset.
**_For example,_**
Suppose most of the prices of houses in a residential property dataset range from 100,000 shillings to 800,000 shillings. However, there is a house priced at 2,000,000 shillings. The price of this house will be considered a global outlier because it is significantly different from the majority of the residential property prices in the dataset. This might affect the overall distribution and analysis of the data.

1. **Contextual outliers**
They are data points that are specific to a subset of the data. This means they exhibit unusual deviation within a specific subgroup or subset of data
**_For instance,_** 
In a study of average household electricity usage,a sudden spike in usage during a particular month due to a heatwave could be a contextual outlier within the broader dataset

1. **Collective outliers**
These are group of data points that collectively form an outlier, even though individually they may not be considered outliers. This type of outlier is often overlooked but has the potential to significantly impact analysis.
_**For example,**_
In a customer satisfaction survey, most responses are moderate. Yet, a subset of responses from a specific demographic consistently rates the product or service much lower. Individually, these responses may not seem unusual, but together they form a distinct outlier group. This could highlight a particular issue or dissatisfaction trend within that demographic, prompting further investigation for targeted improvements in marketing strategies.


1. **Temporal outliers**
Temporal outliers are data points that are outliers with respect to time
_**For example,**_
In stock market ,a sudden and drastic fluctuation in stock prices due to a market event can be considered a temporal outlier.


![types of outliers](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/ukah45m4ioq2rtegwfl6.png)Image by [shailesh](https://www.analyticsvidhya.com/blog/author/shailesh5786337/)



## Why outliers matter
Understanding outliers is crucial across various fields due to their potential to significantly impact data analysis and interpretation. 
They can reveal underlying issues which might otherwise go unnoticed, thereby influencing decision-making.

**In finance,**for instance,outliers can represent unexpected market events that influence investment strategies.
**In healthcare**,outliers can signify unusual patient's responses to certain treatment procedures
**In education**,classroom test scores could represent an outlier and reveal that a certain student might need additional support.

## Identifying and managing outliers

Different methods are used to identify outliers such as the use of statistical measures like the interquartile range (IQR) , Z-scores, Grubbs' Test or visual techniques like box plots.

- **The interquartile range**,for example,identifies outliers that fall below Q1 - 1.5 * IQR or above Q3 + 1.5 * IQR, where Q1 and Q3 represent lower and upper quartiles respectively.

- **Z-scores** on the other hand ,measures the standard  deviation a data point is from the mean of a data set.Data points with Z-scores beyond a certain threshold (typically ±3) are considered outliers.

After identifying the outlier,the question becomes how  to manage the outliers. Should they be removed,transformed or kept-as-is? The answer depends on the circumstances and the impact of the outliers on the analysis or decision making process.

Let's discuss some of the methods used to manage outliers:

- **Removal:**
 Removing outliers from the dataset may help mitigate outliers influence on statistical analyses that are sensitive to extreme values. However,this approach may lead to loss of valuable information and potential bias in the remaining dataset.

- **Transformation:**
 Transforming data using mathematical functions such as square root,logarithmic functions can sometimes normalize the distribution and reduce the impact of outliers.

- **Retention:**
 Sometimes,outliers may represent important observations that should not be discarded. Understanding the context and reason behind outliers can provide valuable insights.

- **Imputation**
This involves replacing outlier values with estimated values based on the surrounding data points. This method preserves the dataset size and structure while reducing the influence of outliers on statistical measures.

Choosing the appropriate method of managing outliers requires careful consideration of the dataset characteristics ,analysis goals and potential implications of the outlier management method. Effective outlier management improves accuracy and reliability of data-driven decisions across different fields.


## Conclusion

In conclusion, outliers are a fascinating concept of data analysis with implications across various domains, as discussed above. They offer valuable insights when understood and managed effectively. 
Understanding outliers is not just about statistical analysis but serves as a fundamental tool in comprehending the world.

Next time you encounter an outlier in a dataset, take a moment to appreciate the insights it can provide and the stories it can tell.

Happy analyzing everyone😃! Remember to like❤️, follow, and comment for more content on data science.

Goodbye👋!