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        <r:String xml:lang="sv">Pre-registrering: Effekter av skolstartstider på ungdomars sömn i gymnasieskolor i Stockholm</r:String>
        <r:String xml:lang="en">Pre-registration: Effects of school start times on adolescent sleep in Stockholm high schools</r:String>
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          <r:String xml:lang="sv">Karolinska Institutet</r:String>
          <r:String xml:lang="en">Karolinska Institutet</r:String>
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        <r:PublisherName>
          <r:String xml:lang="sv">Karolinska Institutet</r:String>
          <r:String xml:lang="en">Karolinska Institutet</r:String>
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        <r:SimpleDate>2026-09-04</r:SimpleDate>
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      <r:Content xml:lang="sv">För pre-registreringens syfte innehåller de filer som tillhandahålls i detta skede enbart simulerade data. De simulerade datafilerna speglar strukturen, variablerna, formaten och de förväntade fördelningarna i de verkliga data som senare kommer att analyseras. Simuleringen baseras på observerade parametrar från klassernas scheman (School start times.csv) samt publicerade skattningar av sömnlängd hos svenska ungdomar (Lemke et al., 2023).

Detta dataset är kopplat till en longitudinell observationsstudie som undersöker sambandet mellan skolstartstider (SST) och sömn hos gymnasieelever i Stockholm, Sverige. 

Stockholms stad har under läsåret 2025/26 infört senare skolstartstider (tidigast kl. 09.00) i utvalda klasser på tre gymnasieskolor. Detta har skapat variation i skolstartstider mellan klasser, vilket möjliggör en observationsbaserad utvärdering av hur skolstartstider påverkar ungdomars sömn. Studien utnyttjar den naturligt förekommande variationen i skolstartstider mellan klasser, där vissa klasser har försenade skolstarter medan andra har behållit sina ordinarie scheman. Skolstartstid behandlas som en kontinuerlig exponering på klassnivå.

Data samlades in från n = 527 gymnasieelever (årskurs 2) i 20 klasser på tre skolor i Stockholm. Enkätdata samlades in vid fyra mättillfällen: vid terminens början (baslinjemätning) samt efter 1, 3 och 6 månaders uppföljning. Det primära utfallet i denna förregistrering är sömnlängd på vardagar, mätt med självrapportering via Karolinska Sleep Questionnaire (KSQ).
Exponeringsvariabeln är klassens genomsnittliga skolstartstid per vecka, beräknad utifrån klasscheman och uttryckt i timmar från midnatt, centrerad vid kl. 08.00.

Studien använder en bayesiansk multilevelmodell (tre nivåer: mättillfällen inom elever inom klasser), implementerad i R med hjälp av paketet brms. Saknade data hanteras genom modellbaserad imputering i brms.</r:Content>
      <r:Content xml:lang="en">For the purpose of pre-registration, the files provided at this stage contain simulated data only. The simulated data mirror the structure, variables, formats, and expected distributions of the real data that will be analysed. The simulation is grounded in observed parameters from the class schedules (School start times.csv) and published estimates of sleep duration in Swedish adolescents (Lemke et al., 2023).

This dataset is connected to a longitudinal observational study examining the association between school start times (SST) and sleep in upper secondary students in Stockholm, Sweden. 

Stockholm City has implemented delayed school start times (no earlier than 9:00 a.m.) in selected classes across three upper secondary schools during the 2025/26 academic year. This created variation in start times across classes, enabling an observational evaluation of how SST affects adolescents' sleep. The study uses naturally occurring variation in school start times across the classes, those with delayed SST and a selection of classes that maintained their original schedules, treating SST as a continuous class-level exposure variable.

Data were collected from n=527 upper secondary students (gymnasium, year 2) across 20 classes in three schools in Stockholm. Questionnaire data were collected at four time points: at the start of the school term (baseline), and at 1, 3, and 6 months follow-up. The primary outcome for this pre-registration is weekday sleep duration, measured via self-report using the Karolinska Sleep Questionnaire (KSQ). The exposure variable is the weekly average school start time per class, derived from class schedules, expressed in hours from midnight and centered at 8:00 a.m.

The study uses a Bayesian multilevel modelling approach (three-level: measurement occasions nested within students nested within classes), implemented in R using the brms package. Missing data are handled via model-based imputation in brms.</r:Content>
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