SFR/ vs. 12 + log(O/H) for our sample and additional galaxies from the literature. As discussed in Sect. 2.2, we include I Zw 18 as one of our sources (see also Schruba et al. 2012). The open triangles for Schruba et al. (2012) correspond to their compilation of literature data and the filled ones to their metal-poor dwarf observations. CO non-detections are shown by upward arrows. The two horizontal dashed lines correspond to the regressions with unit slope shown in Fig. 4, and the dotted one to a robust regression as described in the text: log(SFR/) = (− 2.25 ± 0.15) [12 + log(O/H)] + (11.31 ± 1.3).