Comparison between [OIII] line luminosity and radio luminosity (NVSS) of the WATCAT, FRICAT, and FRIICAT samples (green diamonds, black dots, and red squares, respectively). The turquoise line shows the linear correlation between these two quantities derived from the FR Is of the 3C sample (Buttiglione et al. 2010). No correlation between νL_ν and L_[OIII] can be seen for WATCAT (as for FRICAT) where, at a given line luminosity, the radio luminosities span 1–1.5 orders of magnitude.