Top panel: observed X-ray to optical ratio as in Fig. 8, shown here as a function of optical variability significance and is color-coded as a function of the significance of AGN-like (compared to non-AGN-like) variability. Only non-X-ray-detected galaxies from Baldassare et al. (2018) and Baldassare et al. (2020) are color-coded. X-ray detections are shown with red squares. Bottom panel: same as the top panel, but as a function of baseline in years of the optical light curve, color-coded by the number of data points.