Quartile

Reviewed by Sujaini | Updated on Aug 27, 2020

Catalogue

What is Quartile?

A quartile is a statistical term that defines a division of observations into four specified intervals based on data values, and how they compare with the whole set of observations. To understand the quartile, it is essential to see the median as a central tendency index. In statistics, the median is the mid-value of a number range. It is the point where exactly half of the data lies below the central value and above. Given a set of 13 numbers, the seventh number would be the median. The 6 numbers preceding this value are the lowest data numbers, and the six digits after the median are the highest data set numbers given.

Since extreme values or outliers do not influence the median in the distribution, it is often favoured over the mean.

The median is a reliable position estimator but doesn't tell much about how the data are scattered or distributed on either side of its value. This is here where the quartile comes in. Through splitting the distribution into four classes, the quartile calculates the spread of values above and below the mean.

How Quartiles Work

Just like the median divides the data into half so that 50 per cent of the measurement is below the median and 50 per cent above it, so the quartile divides the data into quarters so that 25 per cent of the measurement is below the lower quartile, 50 per cent below the mean and 75 per cent below the upper quartile.

A quartile divides data into three points-a lower quartile, median, and upper quartile-to form four data set groups. The lower quartile or first quartile is referred to as Q1 and is the middle number that falls between the data set's smallest value and the median.