IQR

Assuming data follows a gaussian distribution, the IQR covers the range between the Q1 and Q3. It's very easily to compute: $\text{IQR} = \text{Q3} - \text{Q1}$.

Once the IQR is known, we can classify as anomaly every value:

• Higher than $Q3 + 1.5 \text{ IQR}$

• Lower than $Q1 - 1.5 \text{ IQR}$

Credit: Wikipedia