Comparison of cluster and primary CMB constraints in the base ΛCDM model, expressed in terms of the mass bias, 1−b. The solid black curve shows the distribution of values required to reconcile the counts and primary CMB in ΛCDM; it is found as the posterior on 1−b from a joint analysis of the Planck cluster counts and primary CMB when leaving the mass bias free. The coloured dashed curves show the three prior distributions on the mass bias listed in Table 2.