Data and the relative linear relations, plotted in red for ODR and in blue for BAY method. The top panels refer to the whole sample, where color coding is according to the log of the effective SFE, readable in the color bar. Data and fits in the middle panels refer to the inner disk and are color coded with a third variable as indicated by the color bar: either log Σ_HI in M_⊙ pc⁻² or σ_HI in km s⁻¹. In the bottom panel, we display the data relative to the outer disk with the relative rms. In all panels, the dashed contours are drawn according to the density of data in the plane.