Results for the reclassified MW sample: PW relations. The colour code is as in Fig. 1. Top and bottom panels: complete sample and that with relative error on parallax better than 20%, respectively. The solid lines represent the least-squares fit to the data obtained with the ABL method (see text). The PW relations are of the form W_A = α + β log P. Left panels: PW relations obtained with β coefficient treated as unknown parameter in Eq. (7). Right panels: β coefficient fixed and equal to that obtained from the LMC.