title: Choice of statistical method influences apparent association between structure and function in glaucoma.
abstract: OBJECTIVE
  The aim of this study was to explore how different statistical methods may lead to inconsistent inferences about the association between structure and function in glaucoma.
  
  
  METHODS
  Two datasets from published studies were selected for their illustrative value. The first consisted of measurements of neuroretinal rim area in the superior-temporal sector paired with the corresponding visual field sensitivity. The second consisted of measurements of average retinal nerve fiber layer thickness over all sectors paired with the corresponding visual field sensitivity. Statistical methods included linear and segmented regression, and a nonparametric local-linear fit known as loess. The analyses were repeated with all measurements expressed as percent of mean normal.
  
  
  RESULTS
  Slopes from linear fits to the data changed by a factor of 10 depending on the linear regression method applied. Inferences about whether structural abnormality precedes functional abnormality varied with the statistical design and the units of measure used.
  
  
  CONCLUSIONS
  The apparent association between structure and function in glaucoma, and consequent interpretation, varies with the statistical method and units of measure. Awareness of the limitations of any statistical analysis is necessary to avoid finding spurious results that ultimately may lead to inadequate clinical recommendations.
authors: Indiana University School of Optometry, Bloomington, IN, USA. imarinfr@indiana.edu
authors: Iván
authors: I
authors: Marín-Franch
authors: Rizwan
authors: R
authors: Malik
authors: David P
authors: DP
authors: Crabb
authors: William H
authors: WH
authors: Swanson
mesh_terms: D005901:Glaucoma / Q000473:pathology* / Q000503:physiopathology*; D006801:Humans; D009412:Nerve Fibers / Q000473:pathology*; D009898:Optic Disk / Q000473:pathology*; D012044:Regression Analysis; D013223:Statistics as Topic / Q000379:methods*; D014786:Vision Disorders / Q000503:physiopathology; D014794:Visual Fields / Q000502:physiology*
keywords: loess; ordinary least-squares regression; segmented regression; structure-function relationships
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