when the data points are arranged in increasing order data are divided into four sections of 25 of the data each 
understanding quartilesto understand the quartile it is important to understand the median as a measure of central tendency the median in statistics is the middle value of a set of numbers it is the point at which exactly half of the data lies below and above the central value the median is a robust estimator of location but says nothing about how the data on either side of its value is spread or dispersed that s where the quartile steps in the quartile measures the spread of values above and below the median by dividing the distribution into four groups they are grouped into four sections of 25 of the data with the second and third groups representing the interquartile range just like the median divides the data into half so that 50 of the measurement lies below the median and 50 lies above it the quartile breaks down the data into quarters so that 25 of the measurements are less than the lower quartile 50 are less than the median and 75 are less than the upper quartile there are three quartile values a lower quartile median and upper quartile which divide the data set into four ranges each containing 25 of the data points calculating quartiles in a spreadsheetsuppose you have a distribution of math scores in a class of 19 students you d want to enter them into a spreadsheet in ascending order in a row you can also use a column use the median function to get the median value then use the quartile function to return the values for each quartile where the second variable in the function is the quartile you re calculating for in this example you should end up with the values for each quartile there is no need to calculate the fourth quartile because it is the last value in your dataset you can see that the first quartile contains scores between 59 and 68 5 and the second quartile scores between 68 5 and 75 the third quartile contains scores between 75 and 81 75 it can help to visualize it calculating quartiles manuallyquartile manual calculation requires more effort as there are formulas involved using the same values as in the spreadsheet example using the following formulas you calculate each quartile 