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Case–control or cohort study?
  1. Tamhane Ashutosh,
  2. Gerald McGwin
  1. Department of Epidemiology, The University of Alabama at Birmingham, Birmingham, Alabama, USA
  1. Correspondence to Ashutosh Tamhane, 1665 University blvd, RPHB 514-A, Birmingham, AL 35294, USA; tamhane{at}

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In a recently published article by Chandra et al the authors have stated that they conducted a ‘case-controlled’ study to examine the anticoagulant effect of warfarin in vitreoretinal surgery.1 However, this study was conducted on a cohort of patients receiving pars plana vitrectomy (PPV); 60 patients who received warfarin (exposure) on the day of …

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  • Competing interests None.

  • Provenance and peer review Not commissioned; not externally peer reviewed.