Percentiles and Quartiles (Jump to: Lecture | Video )

For the following data set:

1, 2, 3, 4, 5

What percent of the numbers are even?

Figure 1.

40% of the values are even.

Percentile

A percentile is a value below which a certain percentage of observations lie.

For the following data set:

2, 2, 3, 4, 5, 5, 5, 6, 7, 8, 8, 8, 8, 8, 9, 9, 10, 11, 11, 12

What is the percentile< ranking of "10"?

Figure 2.

Now, what value exists at the percentile ranking of 25%?

Figure 3.

Here, it is saying that the 25% percentile exists somewhere between the 5th and 6th value. There is no "5.25th" value, so I take the average of the 5th and 6th values to find what value exists at the 25th percentile. 5 and 5 average to give us an answer of 5.

Quartile

Quartiles divide data sets into quarters. There are three quartiles: The 1st Quartile is located at the 25th percentile, the 2nd Quartile is located at the 50th percentile, and the 3rd Quartile is located at the 75th percentile.

Figure 4.

Back to Top