# Quintiles: Overview, Common Uses, and Alternatives

![Quintiles](https://www.investopedia.com/thmb/FfZ0ypzXnD_-T9PjJvnvznMSjvU=/1500x0/filters:no_upscale():max_bytes(150000):strip_icc()/Quintiles_4-3_Final_4190554-572e8479b20e4346a4cae3baeee45477.png)

*— Investopedia / Paige McLaughlin*

> **Definition**
>
> Quintiles break data up into five sequential groups of data.

## What Are Quintiles?

A quintile is defined as “equal-sized segments of a population.” It’s one of five values that divide a range of data into equal parts. The first quintile represents the lowest fifth of the data (1% to 20%), the second quintile represents the second fifth (21% to 40%), and so on to 100%.

![Image](https://www.investopedia.com/thmb/SDQ7HPr6CiQOz1K5wI3v8umNyCw=/1500x0/filters:no_upscale():max_bytes(150000):strip_icc()/dotdash_final_Quintiles_Apr_2020-01-e7580138c92b48a2b945f57beedcd45c.jpg)

*A statistical average falls in the middle of five quintiles.*

Quintiles are used to create cutoff points for a given population; a government-sponsored socioeconomic study may use quintiles to determine the maximum wealth a family could possess to belong to the lowest quintile of society. This cutoff point can then be used as a prerequisite for a family to receive a special government [subsidy](https://www.investopedia.com/terms/s/subsidy.asp) aimed at helping society’s less fortunate.

### Key Takeaways

*   Quintiles are generally used for large data sets.
*   They're often invoked by politicians and economists to discuss economic and social justice concepts.
*   Quartiles and tertiles are alternatives to quintiles that are based on fewer data sets.

## Understanding Quintiles

One of the most common metrics in statistical analysis, the median, is just the result of dividing a population into two quantiles. A quintile is one of five values that divide a range of data into five equal parts, each being one-fifth (20%) of the range. A population split into three equal parts is divided into tertiles, while one split into fourths is divided into [quartiles](https://www.investopedia.com/terms/q/quartile.asp). The larger the data set, the easier it is to divide into greater quantiles. Economists often use quintiles to analyze very large data sets, such as the population of the United States.

For example, if we were to look at all of the closing prices for a specific stock for every day in the last year, the top 20% of those prices would represent the upper quintile of the data. The bottom 20% of those prices would represent the lower quintile of the data. There would be three quintiles in between the upper and lower quintiles. While the average of all the stock prices typically falls between the second and fourth quintiles, which is the middle point of the data, outliers on either the high end or the low end of the data may increase or decrease the average value. As a result, it is worth considering the distribution of the data points—and accounting for any significant outliers—when trying to understand the data and the average values.

## Common Uses of Quintiles

Politicians invoke quintiles to illustrate the need for policy changes. For example, a politician who champions economic justice can divide the population into quintiles to illustrate how the top 20% of income earners control what is, in their opinion, an unfairly large share of the wealth. On the other end of the spectrum, a politician calling for an end to progressive taxation might use quintiles to make the argument that the top 20% shoulder too large a share of the tax burden.

In _The Bell Curve_, a 1994 book on intelligence quotient (IQ), the authors use quintiles throughout the text to illustrate their research, which contends that IQ is heavily correlated with positive outcomes in life. The assertions, however, have been disputed and are considered controversial.

## Alternatives to Quintiles

For certain populations, the use of other methods to examine how the data is distributed makes more sense than using quintiles. For smaller data sets the use of quartiles or tertiles helps prevent the data from being spread too thin. Comparing the [mean](https://www.investopedia.com/terms/m/mean.asp), also known as the “average,” of a data set to its [median](https://www.investopedia.com/terms/m/median.asp), which is the cutoff point where the data is divided into two quantiles, reveals if the data is evenly distributed or skewed toward the top or bottom. A mean that is significantly higher than the median indicates the data is top-heavy, while a lower mean suggests the opposite.

## What Is a Quintile?

If you divide a data set into five equal parts, each one is a quintile.

## What Is a Fifth Quintile?

The fifth quintile is the top data set out of five.

## What Is a Tertile?

If you divide a data set into three equal parts, each one is a tertile. It is used for smaller data sets, where dividing into five parts might stretch the data too thin.

## The Bottom Line

A quintile is one-fifth of a data set or 20%. It’s often used to analyze large data sets, such as the population of a country. Politicians might use quintiles to argue for such laws as progressive taxation, using them to show that the upper portion of the population controls too much wealth as opposed to the lower portions. This in turn could lead to advocacy for government subsidies or even the redistribution of wealth through changes in tax policy.  

> **Article Sources**
>
> 1.  Cambridge Dictionary. "[Quintile](https://dictionary.cambridge.org/dictionary/english/quintile)."
>     
> 2.  Brookings Institute. "[Does 'The Bell Curve' Ring True? A Closer Look at a Grim Portrait of American Society](https://www.brookings.edu/articles/does-the-bell-curve-ring-true-a-closer-look-at-a-grim-portrait-of-american-society/)."