Sleep indices (PSQI, MTCQ, ESS)

During follow-up questionnaire 1B adult Lifelines participants completed questionnaires from the Pittsburgh Sleep Quality Index. Researchers from Erasmus MC used these questions to calculate the Pittsburgh Sleep Quality Index (PSQI), Munich Chronotype Questionnaire (MCTQ), and Epworth Sleepiness Scale (ESS). This syntax has been checked by Lifelines and some bugs have been removed (sections: Lifestyle & environment (Sleep quality (PSQI, Chronotype (MCTQ), Sleepiness (ESS)) and secondary & linked variables).

The sleep indices can be requested in the Lifelines catalogue. When this data has been used in your research, you will have to include a reference to the the following paper:

• Kocevska, D., Lysen, T. S., Dotinga, A., Koopman-Verhoeff, M. E., Luijk, M. P., Antypa, N., ... & Tiemeier, H. (2020). Sleep characteristics across the lifespan in 1.1 million people from the Netherlands, United Kingdom and United States: a systematic review and meta-analysis. Nature human behaviour, 1-10. DOI: https://doi.org/10.1038/s41562-020-00965-x

The PSQI is a self-rated questionnaire which assesses sleep quality and disturbances over a 1-month time interval. Where nineteen questions generate seven 'component' scores. The sum of these scores gives the global PSQI score (Buysse et al., 1989).

The seven 'component' scores were calculated according to the scoring instructions that can be found in the Buysse et al., 1989.

• Component 1: Subjective sleep quality
• Component 2: Sleep latency (cut-off 2.1: >300 minutes to fall asleep)
• Component 3: Sleep duration (cut-off: =< 2 hours and >=20 hours of actual sleep)
• Component 4: Habitual sleep efficiency (cut-offs: bed-time between 12h-17h, waketimes between 20h-24h, awake time >4 hours)
• Component 5: Sleep disturbances (cut-off: >3 missing subcomponents)
• Component 6: Using of sleeping medication
• Component 7: Daytime dysfunction

Afterwards, the global PSQI score was calculated by adding the seven component scores (cut-off: max 1 missing component score). This calculation included a weighing component as well, entailing that in case of six components the global PSQI score has been mulitplied by 7/6.
Result: >121,000 calculated PSQI scores (>109,000 with no missing component score).

Remarks researcher:

1. A major difficulty in coding sleep data from the PSQI is dealing with incoherent sleep times. Per participant qualitative analyses of values may reveal whether the actual reporting was valid but subsequent coding is biased (e.g. typo's somewhere in the data collection procedures), or reporting itself is biased/misclassified (e.g. random error or related to cognitive impairment/illiteracy). For this PSQI score, arbitrary cut-offs were chosen to classify individuals' bed/wake times and subsequent sleep continuity estimates (see cut-offs listed above). These are a compromise between limiting bias and including as many participants.
2. Researchers using the Lifelines' sleep data may choose cut-offs differently, depending on the research question (i.e. limiting implausible reporting more in the context of investigating sleep's association to cognitive impairment or related symptoms/disorders).
3. Some questions for the PSQI are included in the MCTQ. As the MCTQ more broadly queries time-related questions about sleep behaviour, these questions must be used to calculate PSQI component scores and sumscore of subjective sleep quality.

The MTCQ is a questionnaire that assesses sleep and wake behavior on work and free days (Roenneberg et al., 2012). MCTQ provides measures of midpoint of sleep on free days (MSF), and MSF corrected for sleep debt accumulated during the week (MSFsc).

For an overview of the used formulas for the Munich Chronotype estimation we refer to the supplementary material of the article from Roenneberg et al., 2012 and the provided syntax on the workspace. In the end, the social jetlag has been calculated for >104,000 participants.

1. Exclusion criteria for further analyses include:

• persons with use of alarm on free days
• sleep offset work days >12:00
• average sleep durationoutside the range of 3-13 hours

• sleep duration on free days of <3 hours
• sleep duration on work days <3 hours or >13 hours
• MSF > 12.00

2. The questionnaire did NOT include specific questions for shift workers

The eight ESS item scores provide estimates of eight different situational sleep propensities (SSPs) for a person, while the total ESS score gives an estimate of a more general characteristics, the person's 'average sleep propensity' (ASP), across a wide range of activities in their daily lives (ESS website).

Calculation of the ESS score was executed in three steps:

1. Changing the values of each ESS item score the answers (from 1-4 to 0-3)
2. Calculating the overall ESS score by adding the item scores (cut-off: >= 1 item score missing)
3. Categorization of ESS scores according to the ESS website:

• 0-5 ESS score: Lower Normal Daytime Sleepiness
• 6-10 ESS score: Higher Normal Daytime Sleepiness
• 11-12 ESS score: Mild Excessive Daytime Sleepiness
• 13-15 ESS score: Moderate Excessive Daytime Sleepiness
• 16-24 ESS score: Severe Excessive Daytime Sleepiness

Result: >95,000 calculated ESS scores.