Best measure of spread when data is skewed?

• A. Range
• B. Standard deviation
• C. IQR
• D. Variance

Answer: (C)

When data are skewed, look for a measure of spread that isn’t dragged by extreme values. The interquartile range does just that: it measures the spread of the central 50% of the data by taking the difference between the upper and lower quartiles. Because it uses only the middle portion, it stays steady even if there are outliers or a long tail, making it a more reliable sense of how spread out the bulk of the data is. In contrast, the range depends on the extreme values, and the standard deviation and variance include every data point, so they get pulled by outliers and skew. That’s why the interquartile range is the best choice for skewed data.