Zunker, M., H. K. Althoff, J. Apel, H. S. Lässig, L. Schültke, and M. Schredl. “Comparing Questionnaire and Diary Measures for Eliciting Nightmare Frequency”. International Journal of Dream Research, vol. 8, no. 2, Nov. 2015, pp. 129-34, doi:10.11588/ijodr.2015.2.23395.