Measuring Nightmare Frequency: Retrospective Questionnaires Versus Prospective Logs

Retrospective measurements underestimate nightmare frequency, but little is known about how retrospective duration and attention for nightmares may affect this process. This study evaluates the differences between two retrospec- tive durations, a prospective log, and a retrospective estimate after keeping this log. Forty-nine participants completed the SLEEP-50, kept a nightmare log, and estimated their nightmares after keeping a log. Paired t-tests showed that estimates of nightmare frequencies differed significantly from each other according to measurement type (p < .05). Prospective logs are the most accurate way of estimating nightmare frequency, possibly due to simply forgetting over time. For treatment studies relying solely on retrospective measurements, a short duration is recommended.