Descriptive Statistics and Introduction to Probability Practice Test 2026 - Free Practice Questions and Study Guide

The IQR measures how spread out the middle half of the data is. It focuses on the central portion from the 25th percentile up to the 75th percentile. By subtracting the first quartile from the third quartile, you get the distance that covers the middle 50% of observations. For example, if Q1 is 10 and Q3 is 20, the IQR is 10, meaning the central half of the data spans 10 units.

This choice makes sense because it ignores the extremes, which can distort overall spread, and it directly quantifies the width of the central block where most data lie. The other options mix in the median or compare non-central parts, so they don’t measure the central 50% spread.