title: Impact of Study Design on Reported Incidences of Acute Mountain Sickness: A Systematic Review.
abstract: OBJECTIVE
  Published incidences of acute mountain sickness (AMS) vary widely. Reasons for this variation, and predictive factors of AMS, are not well understood. We aimed to identify predictive factors that are associated with the occurrence of AMS, and to test the hypothesis that study design is an independent predictive factor of AMS incidence. We did a systematic search (Medline, bibliographies) for relevant articles in English or French, up to April 28, 2013. Studies of any design reporting on AMS incidence in humans without prophylaxis were selected. Data on incidence and potential predictive factors were extracted by two reviewers and crosschecked by four reviewers. Associations between predictive factors and AMS incidence were sought through bivariate and multivariate analyses for different study designs separately. Association between AMS incidence and study design was assessed using multiple linear regression.
  
  
  RESULTS
  We extracted data from 53,603 subjects from 34 randomized controlled trials, 44 cohort studies, and 33 cross-sectional studies. In randomized trials, the median of AMS incidences without prophylaxis was 60% (range, 16%-100%); mode of ascent and population were significantly associated with AMS incidence. In cohort studies, the median of AMS incidences was 51% (0%-100%); geographical location was significantly associated with AMS incidence. In cross-sectional studies, the median of AMS incidences was 32% (0%-68%); mode of ascent and maximum altitude were significantly associated with AMS incidence. In a multivariate analysis, study design (p=0.012), mode of ascent (p=0.003), maximum altitude (p<0.001), population (p=0.002), and geographical location (p<0.001) were significantly associated with AMS incidence. Age, sex, speed of ascent, duration of exposure, or history of AMS were inconsistently reported and therefore not further analyzed.
  
  
  CONCLUSIONS
  Reported incidences and identifiable predictive factors of AMS depend on study design.
authors.affiliation: 1 Faculty of Medicine, University of Geneva , Geneva, Switzerland .
authors.forename: Baptiste
authors.initials: B
authors.lastname: Waeber
authors.affiliation: 1 Faculty of Medicine, University of Geneva , Geneva, Switzerland .|2 Institute of Sports Sciences and Department of Physiology, University of Lausanne , Lausanne, Switzerland .
authors.forename: Bengt
authors.initials: B
authors.lastname: Kayser
authors.affiliation: 3 Division of Anesthesiology, Geneva University Hospitals , Geneva, Switzerland .
authors.forename: Lionel
authors.initials: L
authors.lastname: Dumont
authors.affiliation: 3 Division of Anesthesiology, Geneva University Hospitals , Geneva, Switzerland .
authors.forename: Christopher
authors.initials: C
authors.lastname: Lysakowski
authors.affiliation: 1 Faculty of Medicine, University of Geneva , Geneva, Switzerland .|3 Division of Anesthesiology, Geneva University Hospitals , Geneva, Switzerland .
authors.forename: Martin R
authors.initials: MR
authors.lastname: Tramèr
authors.affiliation: 3 Division of Anesthesiology, Geneva University Hospitals , Geneva, Switzerland .|4 Institute of Global Health, University of Geneva , Geneva, Switzerland .
authors.forename: Nadia
authors.initials: N
authors.lastname: Elia
mesh_terms: D000531:Altitude; D000532:Altitude Sickness / Q000453:epidemiology*; D015331:Cohort Studies; D000068598:Data Accuracy; D005544:Forecasting; D006801:Humans; D015994:Incidence; D009051:Mountaineering; D012107:Research Design
keywords: acute mountain sickness; altitude; cohort; cross-sectional study; randomized controlled trial