Comparing questionnaire and diary measures for eliciting nightmare frequency
Studies investigating the prevalence of nightmares have generally found higher frequencies in studies using daily logbooks or diaries compared to retrospective reports, raising the question as to whether retrospective questionnaires lead to an underestimation of nightmare frequency, possibly due to the suppression of the frightening nightmare experience or if the diary enhances recall. In this study, 71 participants filled in a questionnaire about their sleep, dreams, and emotions during the day in the beginning phase of the study and were then asked to keep a checklist diary for two weeks. The results show that there is a small but non-significant increase in nightmare estimates and much more pronounced differences in overall dream recall frequency and in other aspects of daily life, such happiness and pain sensations. No effect of emotional tone on the differences in the questionnaire and diary measures was found. The present findings imply that the increase in nightmare frequency using diary measures instead of retrospective questionnaires might be a result of the increase in overall dream recall frequency. The differences in the other variables might be attributable to motivation effects. For future research, we suggest eliciting current stress levels and attitudes toward nightmares in order to study whether these variables might affect the difference between diary and questionnaire measures.