Comparison between the EWs of Hδ, Hβ, Hα and Paβ lines. The blue lines represent the best-fit linear relation, while the blue shaded areas indicate the ±1σ dispersion of the galaxies around the best-fit line. We display in top-left corner of each panel the Spearman correlation coefficient “R” and corresponding “p”-value, the residual χ² of the correlation (“”) and the 1σ scatter around the best-fit line, whose equation (comprising 1σ errors on the best-fit coefficients) is shown in the bottom-right corner. In the four diagrams, all the points with available measurements (excluding upper limits) were used in the fit.