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Thread: vision in eyes at different times

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    vision in eyes at different times




    Hi everyone,

    New to the forum and am seeking a bit of guidance as to how to compare vision (visual acuity) between eyes.
    So I am trying to compare the vision of an eye when a particular complication of a disease develops - lets call this X. This complication X of the disease tends to develop in one eye at a time (first eye), and may develop in the other at sometime in the future (second eye). Both eyes would have started off with the early stages of the disease (i.e. without complication X yet) when the first eye developed complication X).
    So I have the vision from 89 people who developed this complication X in their first eye. I then followed these 89 people for a certain length of time and collected the vision when they developed complication X in their second eye, this ended up being 38 eyes of those original 89 people.

    Now I know eyes from the same person are not "independent", but I initially thought an independent t-test would be a suitable test to compare the visions between the first eyes and the second eyes because the visions were taken at different time points. However, a reviewer has told me that they should be considered "dependent" and that I should be using something like a paired t-test to compare the visions (or a Mann-whitney U test i guess) unless i could provide justification otherwise.

    So if anyone could please advise me as to whether i should be treating these as dependent or independent would (or how else i should be tackling this situation) greatly appreciated.

    Thanks
    Last edited by jksgoh; 03-11-2017 at 02:50 AM.

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    Re: vision in eyes at different times


    If vision varies naturally between subjects, then I would consider the data to be paired and a paired test like the t test or Wilcoxon would be appropriate.

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