The subjective meaning of good sleep, an intraindividual approach using the Karolinska Sleep Diary

The present experiment used an intraindividual design to investigate the meaning and measurement of "good sleep". Each of 16 subjects slept in an isolation unit according to a schedule (15 sleeps) designed to give variable quality of sleep. Self-rated sleep measures (from the Karolinska Sleep Diary) were obtained after each sleep and subjected to intraindividual regression analyses across time. Most subjective sleep measures showed a strong covariation across conditions. Subjective quality of sleep mainly involved variables of sleep continuity, in particular, perceived calmness of sleep and sleep efficiency. "Sleep quality," "calm sleep," "ease of falling asleep," and ability to "sleep throughout" the time allotted strongly covaried and formed an index of sleep quality. Self-rated ease of awakening deviated from the general pattern and was associated with poor sleep quality. So was reported dreaming (related to awakenings). It was concluded that most subjective sleep measures tend to covary across conditions and that "good sleep" is mainly a question of sleep continuity.