Shen, S., White, S. D. M., Mo, H. J., Voges, W., Kauffmann, G., Tremonti, C., & Anderson, S. F. (2006). The soft X-ray properties of quasars in the sloan digital sky survey. Monthly Notices of the Royal Astronomical Society Letters, 369(4), 1639-1653. doi:10.1111/j.1365-2966.2006.10463.x.