Distributions of the Z-scores computed from the injection tests of EW₈₆₂₁, λ₈₆₂₁, and σ₈₆₂₁ as a function of the injected DIB parameters and the S/N of the ISM spectra. The color scale indicates the number density estimated by the Gaussian KDE. In each panel, the solid red line indicates the variation in the mean differences of Z-scores with the injected DIB parameters and the S/N. The solid white line indicates the mean absolute differences of the Z-scores. The dashed red and white lines provide a reference for Z-score equals 0 and ±1.