Question

How does the interquartile range relate to percentiles?

Answer 1

It's the range between the `25th` and `75th` percentile.

Working with quartiles means you order your cases by value and then divide into four equal groups.

The interquartile range (abbreviated as `Q3-Q1`) is the difference between the first quartile and the third, these being the 'border' values between the first quarter and the second, and between the third and fourth.
In this range you'll find `50%` of your values (the second and third quarter of your data).