Kelly, William E., John R. Mathe, and Qiujun Yu. “Specific Versus Scaled Estimates: A Comparison of Two Approaches to Measuring Retrospective Nightmare Frequency”. International Journal of Dream Research 11, no. 2 (November 1, 2018): 203–206. Accessed October 4, 2022. https://journals.ub.uni-heidelberg.de/index.php/IJoDR/article/view/48486.