Derived PL relation for Mira variables. Top: bolometric PL relation based on the luminosity of the Mira variables in the VLBI sample. The red solid line shows the PL relation obtained when using a fixed slope, and the blue dashed line represents the relation obtained when the slope is a free parameter. The sources excluded from the fit are represented by the open symbols. Bottom: comparison between our PL relation with the bolometric PL relations for C-type stars by Feast et al. (2006) in the Milky Way (F06 MW), Whitelock et al. (2006) (W06 LMC), and Whitelock et al. (2009) (W09 LMC) in the LMC.