Distributions of EW of the three spectral lines [O III] (top), of the [N II] doublet and Hα (middle), and of Hβ (bottom), used as determining features for the development of our new diagnostic for the activity classes of star-forming (SF), AGN, LINER, composite, and passive galaxies. All measurements were performed on non-starlight-subtracted SDSS spectra. We adhered to the same conventions as the SDSS, wherein negative EW correspond to emission.