Time-averaged SED of NGC 5548 fitted with Case 1 and Case 3 models, using the best-fit parameters listed in Table 2 (see Sect. 2 for details). The blue data points correspond to the UV/optical data, the black, grey, and orange data points correspond to the Swift/XRT spectra extracted from three different time intervals that are consistent with the average X-ray flux. The bottom panels show the corresponding data-to-model ratios.