Predicted differential number counts normalized to S^-2.5 at 8.44 GHz (left panel) and at 15 GHz (right panel) for the C1 model (thick continuous line), i.e. the model with no difference between the r_M value adopted for FSRQs and BL Lac objects (see text). At 8.44 GHz data points are a collection from different samples (see De Zotti et al. 2010), whereas at 15 GHz they have been computed from the 10C survey. In the left panel predictions for number counts of flat- (short-dashed line) and steep-spectrum (dotted line) sources are also shown, compared with results from measurements at 8.4 GHz of flat-spectrum sources by the CRATES program (empty circular points). Predictions at 15 GHz from the De Zotti et al. (2005) model are also shown (blue dash-dotted line).