Low-resolution power spectra for different values of R_Edd within a narrow range in black hole mass (left) and different black hole masses but similar values of R_Edd (right). The markers represent the median variance (i.e., power × frequency) of all quasars falling in each M − R_Edd bin and temporal frequency, and the error bars represent the root-mean-squared (rms) of the median for each bin obtained by bootstrapping the samples. The power spectra depend on both parameters but in different ways: the mass changes the slope (or the location of the bend in the power spectrum, as described in Sect. 4) and the accretion rate modifies mostly the normalisation, although some change in the slope is apparent. Frequencies are in units of day⁻¹.