Comparing radio loudness R_g, emission line ratio [O III]/Hβ, and spectral index, where available. From the sample of 26 R_g values (Table 1), 7 also have [O III]/Hβ values available (Table 2, alias T2; black bars in central panel), and 9 have fitted α values (Table 3, alias T3). HF indicates spectral indices fitted between 1.4 and 3 GHz. Class 1, 2, and 3 (c1, c2, c3) as defined by Eckart et al. (1986). Unfilled histograms in middle and lower panels represent all available “compact radio source-dwarf galaxy” matches below 3σ on the L–SFR relation.