Using Median Lines in Robust Bivariate Data Analysis

Methods for robust comparison of bivariate errors‐in‐variables are considered. The concept of median lines is introduced for the robust estimation of principal components. Median lines separate the bivariate sample space into two equally sized parts. Statistical properties of the model parameters are derived. Robust residual analysis assesses linear relationships as well as goodness of fit and allows for the detection of potential outliers. Special emphasis is laid on graphical methods. A bivariate box‐plot is proposed for exploratory data analysis. The median lines procedure is illustrated by a real example.