Saris, Willem, Melanie Revilla, Jon A. Krosnick, and Eric M. Shaeffer. “Comparing Questions With Agree/Disagree Response Options to Questions With Item-Specific Response Options”. Survey Research Methods 4, no. 1 (May 1, 2010): 61-79. Accessed June 5, 2020. https://ojs.ub.uni-konstanz.de/srm/article/view/2682.