Comparison of observed periods in rest-frame versus the characteristic periods of accretion discs. Panels (a, b, c, d) are the Keplerian periods at the region for 5100 Å photons (T₅₁₀₀), the critical radius of self-gravity (T_SG), averaged radius (T_mean) and the precessing period of warped discs (T_WD) versus observed periods(T_obs), respectively. Their corresponding histograms are shown in panels (e, f, g, h). Vertical dash lines are the average levels.