In data analysis, what is the interquartile range?

• A. The average of the middle 50%
• B. The standard deviation
• C. The difference between the third and first quartiles (Q3 − Q1)
• D. The range between the minimum and maximum values

Answer: (C)

The interquartile range measures how spread out the middle portion of the data is. It is found by subtracting the first quartile from the third quartile: IQR = Q3 − Q1. This focuses on the central 50% of values, making it robust to outliers. The other descriptors describe different ideas: the average (mean) reflects central tendency, not spread; the standard deviation measures dispersion around the mean and uses all data; the range uses the extreme values (minimum to maximum), which can be heavily influenced by outliers. Therefore, the interquartile range is the difference between the third and first quartiles.