Radio power at 150 MHz of low-frequency radio halos as a function of the PSZ2 mass. The lines indicate the extreme cases of the correlations of radio power to cluster mass reported in van Weeren et al. (2021), which were derived using different fitting methods and samples. The dark blue line shows the steepest (orthogonal method) and the light blue line shows the flattest (including candidate halos, Y|X method) correlation. The shaded regions show the 95% confidence interval. The halos reported as ‘van Weeren+21 & lit.’ include a literature radio halo sample (de Gasperin et al. 2015; Cordey 1985; Wilber et al. 2018; Botteon et al. 2019; Bîrzan et al. 2019; Savini et al. 2018, 2019; Bonafede et al. 2018; Hoang et al. 2019a,b; Macario et al. 2013; George et al. 2017; Duchesne et al. 2021).