Predictions for the GWB characteristic strain amplitude at f = 1/10 yr from a range of SAMs published in the literature, assuming quasicircular orbits and no environmental interactions (i.e. γ = 13/3), but different physical prescriptions for the delays (increasing from left to right) between galaxy mergers and black hole mergers. The “no delays”, “medium delays” and “long delays” models correspond respectively to the classes of models (i), (ii) and (iii) defined in the text. The ranges account for the finite resolution of the models. The shaded area is the DR2new 95% confidence bound. More details about the models are provided in the text.