# Understanding Kurtosis: What it is, Different Types, and Why it Matters.

Article Summary

Kurtosis is a measure of the shape of a probability distribution, specifically its peakedness, and tail-heaviness. It is a useful tool in various fields, including finance, economics, and psychology, to analyze risk, income inequality, and personality traits. Understanding the concept of kurtosis and how to calculate it can help individuals better analyze and interpret their data.

## Understanding kurtosis

Kurtosis is a measure of the shape of a distribution and is often used in conjunction with measures of central tendency such as the mean and median. A distribution with high kurtosis indicates that the distribution has more outliers or extreme values than a distribution with low kurtosis. A distribution with low kurtosis indicates that the data is more spread out and does not have as many extreme values.

Kurtosis is calculated by comparing the distribution to a normal distribution, which has a kurtosis of 0. A positive kurtosis value indicates that the distribution has a sharper peak and heavier tails than a normal distribution, while a negative kurtosis value indicates that the distribution is flatter and has lighter tails.

## Formula and calculation

The formula for calculating kurtosis is as follows:

Kurtosis = [Σ(xi – x̄)^4 / n] / s^4 – 3

Where:

• xi = the value of the ith observation
• x̄ = the mean of the distribution
• n = the sample size
• s = the standard deviation of the distribution

Calculating kurtosis involves four steps:

1. Calculate the mean and standard deviation of the distribution.
2. Calculate the deviation of each value from the mean.
3. Raise the deviations to the fourth power and sum them up.
4. Plug the values into the formula above to calculate kurtosis.

## Types of kurtosis

There are three types of kurtosis: mesokurtic, leptokurtic, and platykurtic. Each type of kurtosis represents a different shape of a distribution.

### Mesokurtic

A mesokurtic distribution is a normal distribution with a kurtosis value of 0. This means that the distribution has a moderate peak and moderate tails, similar to a bell-shaped curve. Most statistical analyses assume that the data is normally distributed, which means it has a mesokurtic shape.

### Leptokurtic

A leptokurtic distribution has a kurtosis value greater than 0. This means that the distribution has a higher peak and heavier tails than a normal distribution. This type of distribution indicates that the data has more extreme values than a normal distribution. In finance, a leptokurtic distribution may indicate higher risk due to the presence of extreme values in a dataset.

### Platykurtic

A platykurtic distribution has a kurtosis value less than 0. This means that the distribution has a lower peak and lighter tails than a normal distribution. This type of distribution indicates that the data has fewer extreme values than a normal distribution. In finance, a platykurtic distribution may indicate lower risk due to the absence of extreme values in a dataset.

Understanding the different types of kurtosis and their implications can help individuals make better decisions when analyzing their data. While a mesokurtic distribution is generally considered to be ideal, it is important to consider the context of the data being analyzed to determine the appropriate type of kurtosis.

## Using kurtosis

Kurtosis can be a useful tool in various fields for analyzing data and making decisions based on the distribution of that data. Here are some examples of how kurtosis is used in different areas:

### Finance

In finance, kurtosis is used to analyze risk in investment portfolios. A higher kurtosis value indicates that the distribution of returns has more extreme values, which can increase the risk of the portfolio. Financial analysts can use kurtosis to identify potentially risky investments and adjust their portfolios accordingly.

### Economics

Kurtosis is also used in economics to analyze income inequality. A high kurtosis value in income distribution indicates that there are more people in the extreme ends of the income spectrum, with a small middle class. This can have implications for social and economic policies that aim to reduce income inequality.

### Psychology

In psychology, kurtosis is used to analyze personality traits. A high kurtosis value in a personality trait distribution indicates that there are more people who strongly exhibit that trait, with fewer people in the middle range. This can help psychologists better understand and diagnose personality disorders.

### Data analysis

Kurtosis can also be used in data analysis to identify outliers and assess the normality of a distribution. A high kurtosis value can indicate that the data deviates significantly from a normal distribution, which may affect the validity of statistical tests that assume normality.

Overall, kurtosis can provide valuable insights into the distribution of data in various fields. However, it is important to consider the context of the data being analyzed and to use kurtosis in conjunction with other statistical measures to make informed decisions.

## Kurtosis FAQs

### What is a good kurtosis value?

A kurtosis value of 0 indicates that the distribution is normal. Positive values indicate a sharper peak and heavier tails, while negative values indicate a flatter distribution with lighter tails. There is no specific range of kurtosis values that is considered “good” or “bad,” as it depends on the context of the data being analyzed.

### Can kurtosis be negative?

Yes, kurtosis can be negative. A negative kurtosis value indicates that the distribution is flatter and has lighter tails than a normal distribution.

### What is the difference between kurtosis and skewness?

While kurtosis measures the peakedness and tail-heaviness of a distribution, skewness measures the asymmetry of a distribution. A distribution with positive skewness is skewed to the right, while a distribution with negative skewness is skewed to the left.

### How does kurtosis relate to standard deviation?

Kurtosis and standard deviation are both measures of the spread of a distribution. However, kurtosis specifically measures the presence of extreme values, while standard deviation measures the overall variability of the data.

## Key takeaways

• Kurtosis is a measure of the peakedness and tail-heaviness of a probability distribution.
• There are three types of kurtosis: mesokurtic, leptokurtic, and platykurtic.
• Kurtosis can be useful in finance, economics, and psychology to analyze risk, income inequality, and personality traits.
• There is no specific range of kurtosis values that is considered “good” or “bad,” as it depends on the context of the data being analyzed.
• Kurtosis and skewness are different measures that describe different aspects of a distribution.
###### View Article Sources
1. Skewness and Kurtosis – National Institute of Standards and Technology
2. Skewness and Kurtosis in Statistics Explained – freeCodeCamp
3. Measures of Skewness and Kurtosis: Their Relationships to Each Other and to Other Summary Statistics – The American Statistician, JSTOR