Article Text

Download PDFPDF
Authors' response
  1. Radouil Tzekov1,
  2. Carol Bigelow2,
  3. Christine Clemson1,
  4. Jenna Checchi1,
  5. Mark Krebs3,
  6. Shalesh Kaushal1
  1. 1Department of Ophthalmology, University of Massachusetts Medical School, Worcester, Massachusetts, USA
  2. 2Division of Biostatistics and Epidemiology, Department of Public Health, University of Massachusetts School of Public Health and Health Sciences, Amherst, Massachusetts, USA
  3. 3Department of Molecular Genetics and Microbiology, University of Florida, Gainesville, Florida, USA
  1. Correspondence to Dr Shalesh Kaushal, Department of Ophthalmology, University of Massachusetts Medical School, Worcester, MA 01605, USA; shalesh.kaushal{at}

Statistics from

Request Permissions

If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.

We appreciate the concerns raised by Sandberg et al in their recent letter1 pertaining to the design and statistical methods of our analysis described in our recent article,2 and we welcome the opportunity to respond to each point raised.

Study design

We agree that ideally the best ‘gold standard’ study design would involve the use of matched controls, matching on eye function at baseline, as we plan to do in our upcoming clinical trial. For preliminary pilot studies, however, other study designs, including methodologies that do not have controls, can also be meaningful, especially when the objectives are to assess treatment potential and establish the equipoise necessary for further investigation in a randomised control study. An example that is relevant to our work is presented by an article from one of the authors of the letter (Rosner et al; Section 4.1),3 in which the investigators assessed the potential benefit of treatment and concluded that their findings were suggestive of a lack of effect due to treatment. These researchers did not have a control group, yet they felt comfortable with the conclusions based on this design. Our analytical design and findings are consistent with this example. Our focus was an exploration of potential therapeutic value, and our detailed description of visual function in 14 eyes establishes a possible treatment benefit that merits a randomised control trial.

Statistical analysis

We believe that the exploration of treatment potential in a sample size of seven is best addressed with detailed descriptions rather than formal tests of statistical significance. Given that significance levels were reported, however, we agree with Sandberg et al that the unit of analysis should have taken into account the correlation structure of the data. We thank Dr Rosner for pointing out the modification of the Wilcoxon signed-rank test for use with …

View Full Text


  • Competing interests None.

  • Provenance and peer review Commissioned; not externally peer reviewed.

  • i Some studies describe doses of 100 mg/kg/day.