April 2009
Volume 50, Issue 13
ARVO Annual Meeting Abstract  |   April 2009
Not Just as Simple as T-Tests!
Author Affiliations & Notes
  • M. R. Stevenson
    Epidemiol & Public Health,
    Queens University, Belfast, United Kingdom
  • U. Chakravarthy
    Centre for Vascular and Vision Sciences,
    Queens University, Belfast, United Kingdom
  • S. Beatty
    Ophthalmology, Waterford Regional Hospital, Waterford, Ireland
  • Footnotes
    Commercial Relationships  M.R. Stevenson, None; U. Chakravarthy, Educational Grant Dr Mann Pharma, F; Bausch and Lomb, C; Bausch and Lomb, R; S. Beatty, Educational Grant Dr Mann PHarma, F; Bausch and Lomb, C; Bausch and Lomb, R.
  • Footnotes
    Support  Supported by an Educational Grant from Dr Mann Pharma
Investigative Ophthalmology & Visual Science April 2009, Vol.50, 5065. doi:
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      M. R. Stevenson, U. Chakravarthy, S. Beatty; Not Just as Simple as T-Tests!. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5065.

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      © ARVO (1962-2015); The Authors (2016-present)

  • Supplements

Purpose: : To report on the statistical methodology used for the analysis of longitudinal functional and morphological outcomes recorded in both eyes of participants enrolled in the CARMA clinical trial.

Methods: : Carotenoids and Co-antioxidants in Age-Related Maculopathy is a randomised double masked prospective trial of L and Z with co-antioxidants; active (A) versus placebo (P). A total of 433 participants were randomised to A or P and followed for up to 3 years (7 visits). The primary outcome was change in best corrected distance visual acuity and secondary outcomes included measures of contrast sensitivity, raman spectroscopy, photopic interferometry, fundus photograding and serum antioxidants. Eligible patients could have one or both eyes entered as study eyes. Correlation coefficients between recorded BCVA for both eyes were generated and weights derived to account for this. The general linear model was used to examine continuous outcomes in a longitudinal time-frame. A 14 point joint nominal and ordinal categorical scale from photograding was re-ordered and condensed to yield a 6 point ordinal scale.

Results: : The correlation between eyes for change in DVA at 12 months was 0.27 showing that when outcomes are obtained from both eyes, the information from the second of the pair is less than that from the first. Weights of 0.81 and 1.27 were computed for participants who contributed one or both eyes to the analysis. Of 1665 visits with morphological data, 8.8% of eyes progressed from less severe to more severe AMD status from one visit to the next. Less than 0.2% of eyes showed a change in the opposite direction.

Conclusions: : The method described allows outcomes recorded from both eyes of participants to be used effectively

Clinical Trial: : www.ISRCTN.org ISRCTN94557601

Keywords: clinical (human) or epidemiologic studies: biostatistics/epidemiology methodology • age-related macular degeneration • antioxidants 

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