title: Sleep Irregularity in the Previous Week Influences the First-Night Effect in Polysomnographic Studies.
abstract: OBJECTIVE
  The first-night effect is a well-known phenomenon resulting from an individual's maladaptation to the unfamiliar environment of a sleep laboratory. However, there have been no direct reports of the effect of previous sleep patterns on the first-night effect. We aimed to investigate the effect the previous week's sleep pattern on the first-night effect.
  
  
  METHODS
  Twenty-four young, healthy, male participants completed the study procedure. During one week prior to study, the participants kept sleep diaries and wore actigraphs to identify sleep-wake pattern. Two consecutive nights of polysomnography were conducted after that. Wilcoxon signed-rank tests were applied to compare sleep variables of the two nights. Variance (standard deviation) of sleep onset time during the previous week was used as an index of irregularity. A Kendall's ranked correlation analysis and a linear regression test were applied to detect correlation between sleep irregularity and the first-night effect measured by polysomnography.
  
  
  RESULTS
  There were significant differences in the values of sleep efficiency (p=0.011) and wake after sleep onset (WASO) (p=0.006) between the two nights. Sleep efficiency was lower and WASO was higher on the first night as compared to the second night. Sleep irregularity in the previous week was negatively correlated with sleep efficiency (p<0.001) of the first night, but was not significantly correlated with any other sleep parameters.
  
  
  CONCLUSIONS
  We replicated the existence of the first-night effect commonly observed in sleep studies. Sleep irregularity in the previous week may influence the first-night effect in polysomnographic studies.
authors.affiliation: Department of Psychiatry, Korea University College of Medicine, Seoul, Republic of Korea.
authors.forename: Da-Hye
authors.initials: DH
authors.lastname: Lee
authors.affiliation: Department of Psychiatry, Korea University College of Medicine, Seoul, Republic of Korea.
authors.forename: Chul-Hyun
authors.initials: CH
authors.lastname: Cho
authors.affiliation: Department of Psychiatry, Korea University College of Medicine, Seoul, Republic of Korea.
authors.forename: Changsu
authors.initials: C
authors.lastname: Han
authors.affiliation: Department of Psychiatry, Korea University College of Medicine, Seoul, Republic of Korea.
authors.forename: Ki-Nam
authors.initials: KN
authors.lastname: Bok
authors.affiliation: Department of Psychiatry, Korea University College of Medicine, Seoul, Republic of Korea.
authors.forename: Jung Ho
authors.initials: JH
authors.lastname: Moon
authors.affiliation: Department of Preventive Medicine, Korea University College of Medicine, Seoul, Republic of Korea.
authors.forename: Eunil
authors.initials: E
authors.lastname: Lee
authors.affiliation: Department of Psychiatry, Korea University College of Medicine, Seoul, Republic of Korea.
authors.forename: Heon-Jeong
authors.initials: HJ
authors.lastname: Lee
authors.affiliation: Department of Psychiatry, Korea University College of Medicine, Seoul, Republic of Korea.
authors.forename: Leen
authors.initials: L
authors.lastname: Kim
keywords: First-night effect; Polysomnography; Sleep efficiency; Sleep irregularity