Tehran University of Medical Sciences Journal of Sleep Sciences 2476-2938 7 3-4 2024 04 13 75 79 William Kelly Department of Clinical Mental Health Counseling, Neumann University, Aston, PA, USA 2023 09 06 2023 10 08 Background and Objective: Nightmare frequency is typically measured using interval and ordinal, but rarely Likert-type, scales. The current study aimed to examine the validity and reliability of a Likert-type measure of retrospective nightmare frequency. Materials and Methods: Participants included a convenience sample of undergraduate students. They completed a recent-ly developed Likert-type nightmare frequency item, an established Nightmare Frequency Scale, an estimate of nightmare frequency over the past week, and measures of hypothetically related variables including neuroticism, psychological dis-tress, and trauma symptoms. Convergent and discriminant validity was evaluated through relationships between the Likert-type nightmare frequency item with other nightmare measures and hypothetically related variables. Reliability was esti-mated using a correction for attenuation approach designed to provide a conservative estimate of single-item reliability. Results: The sample included 233 (119 female, 51.1%; 114 male, 48.9%) university students (mean age: 19.05 ± 1.91). The average convergent validity coefficient between the Likert-type nightmare frequency item and other nightmare measures (r = 0.647) was significantly different (z = 5.45, P < 0.001) from its average correlation coefficient with hypo-thetically related measures (r = 0.256). The single-item reliability coefficient was 0.722. Conclusion: The reliability and convergent and discriminant validity of the Likert-type nightmare frequency item were supported. https://jss.tums.ac.ir/index.php/jss/article/view/268