People differ in their sleep timings that are often referred to as a chronotype and can be operationalized as mid-sleep (midpoint between sleep onset and wake-up). The aims of the present studies were to examine intraindividual variability and longer-term temporal stability of mid-sleep on free and workdays, while also considering the effect of age. We used data from a 2-week experience sampling study of British university students (Study 1) and from a panel study of Estonian adults who filled in the Munich Chronotype Questionnaire twice up to 5 years apart (Study 2). Results of Study 1 showed that roughly 50% of the variance in daily mid-sleep scores across the 14-day period was attributed to intraindividual variability as indicated by the intraclass correlation coefficient. However, when the effect of free versus workdays was considered, the intraindividual variability in daily mid-sleep across 2 weeks was 0.71 the size of the interindividual variability. In Study 2, mid-sleep on free and workdays showed good levels of temporal stability—the retest correlations of mid-sleep on free and workdays were 0.66 and 0.58 when measured twice over a period of 0-1 to 5 years. The retest stability of mid-sleep scores on both free and workdays sharply increased from young adulthood and reached their peak when participants were in late 40 to early 50 years of age, indicating that age influences the stability of mid-sleep. Future long-term longitudinal studies are necessary to explore how age-related life circumstances and other possible factors may influence the intraindividual variability and temporal stability of mid-sleep.

人们的睡眠时间有所不同，这通常被称为睡眠时间类型，并且可以被操作为睡眠中期（睡眠开始和醒来之间的中点）。本研究的目的是检查自由日和工作日睡眠中期的个体差异和长期时间稳定性，同时也考虑年龄的影响。我们使用的数据来自对英国大学生进行的为期两周的经验抽样研究（研究 1）和对爱沙尼亚成年人进行的小组研究，这些成年人两次填写慕尼黑时间型问卷，间隔最多 5 年（研究 2）。研究 1 的结果表明，14 天期间每日睡眠中期评分的大约 50% 的差异归因于个体内部差异，如组内相关系数所示。然而，当考虑空闲时间与工作日的影响时，两周内每天睡眠中期的个体差异是个体间差异大小的 0.71。在研究 2 中，空闲日和工作日的睡眠中段显示出良好的时间稳定性水平——在 0-1 至 5 年的时间内测量两次时，空闲日和工作日的睡眠中段的重新测试相关性分别为 0.66 和 0.58。自由日和工作日的睡眠中期得分的重测稳定性从成年早期开始急剧增加，并在参与者40岁末至50岁出头时达到峰值，表明年龄影响睡眠中期的稳定性。未来的长期纵向研究有必要探索与年龄相关的生活环境和其他可能因素如何影响个体内的变异性和中期睡眠的时间稳定性。