Question 1

Why use IQR instead of standard deviation?

Accepted Answer

IQR is resistant to outliers and does not assume a normal distribution. Standard deviation is affected by extreme values. Use IQR when your data is skewed or contains outliers. Use standard deviation when data is approximately normal and outliers are unlikely.

Question 2

What is the 1.5 × IQR rule?

Accepted Answer

The 1.5 × IQR rule (Tukey's fences) identifies potential outliers. Any value below Q1 - 1.5×IQR or above Q3 + 1.5×IQR is flagged as a mild outlier. Values beyond Q1 - 3×IQR or Q3 + 3×IQR are considered extreme outliers. For a normal distribution, about 0.7% of data falls beyond the 1.5×IQR fences.

Question 3

What is the mid-hinge?

Accepted Answer

The mid-hinge is (Q1 + Q3) / 2, the average of the first and third quartiles. It provides a robust estimate of the center of the data, similar to the median but calculated from the quartiles. For symmetric distributions, the mid-hinge equals the median.

Interquartile Range (IQR) Calculator

Outlier Fences

Advantages of IQR

Frequently Asked Questions