Residual plots. Residual plots for protein CDH13 in the study of breast cancer cell lines. The protein has 16 features, residuals from the same feature have the same color. (a) Residuals versus predicted peak log-abundance. (b) Absolute residuals versus predicted mean peak abundance are modeled by a loess curve. Values on the curve predicted for each LC-MS peak are used as weights in the iterative least squares model fit.