Zunker, M., Althoff, H. K., Apel, J., Lässig, H. S., Schültke, L. and Schredl, M. (2015) “Comparing questionnaire and diary measures for eliciting nightmare frequency”, International Journal of Dream Research, 8(2), pp. 129–134. doi: 10.11588/ijodr.2015.2.23395.