An observation falling outside the limits 

                                                        𝐹𝐿 1. 5(𝐹𝑈 𝐹𝐿), 𝐹𝑈 + 1. 5(𝐹𝑈 𝐹𝐿) 

where F U and F L are the upper and lower quartiles of a sample. Such observations are usually regarded as being extreme enough to be potential outliers.