Spectral properties of SDSS galaxies (grey dots) and QPE hosts (diamonds). Two out of the five QPE hosts lie in a sparsely populated region of this diagram of Hα EW vs. the Lick Hδ_A absorption index. The relative fraction of sources within the coloured boxes is shown: E+A galaxies represent only 0.2% of SDSS galaxies (red dashed box), while quiescent Balmer strong galaxies represent 2.3% (red solid box). The slightly widened (blue) box that encompasses eRO-QPE1 (Hα EW < 4 Å) contains 3.1% of SDSS galaxies.