4.5 Boxplots
Outliers are values that extremely deviate from the mean, i.e., extremely high or low values. Those values limit the explanatory power of the mean. Reasons for outliers can be error in measurement, error of judgement, miscalculation, typo in data matrix, real extraordinary values. To treat outliers, we must know whether they are true values or a mistake. Outliers can be neglected under certain conditions, but it is important to bear them in mind when interpreting results!