Plot of log([O III]λ5007/Hβ) vs. the radio-loudness parameter (L_1.4 GHz/L_{5100 @@@(LBT)}). Green dots represent galaxies with flat radio spectral index (−0.7 ≤ α_1.4/4.85 ≤ −0.4), while red dots represent galaxies with inverted radio spectral index (α > −0.4). The vertical blue line represents the median value of the radio-loudness parameter for the non-radio detected galaxies from Table 31 and the magenta arrows indicate that this is the upper limit of the radio-loudness at the log([O III]λ5007/Hβ) values for each of the galaxies.