alexa Statistical problems caused by missing data resulting from neodymium:YAG laser capsulotomies in long-term posterior capsule opacification studies
Ophthalmology

Ophthalmology

Journal of Clinical & Experimental Ophthalmology

Author(s): Buehl W, Heinzl H, Mittlboeck M, Findl O

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Purpose To describe a way to eliminate the problem caused by missing data due to neodymium:YAG (Nd:YAG) laser capsulotomies before statistical analysis, which leads to incomplete data in long-term studies of posterior capsule opacification (PCO). Setting Medical University of Vienna, Vienna, Austria. Methods To demonstrate the problem, an existing long-term study comparing PCO development in eyes with round-edged and sharp-edged intraocular lenses (IOLs) was analyzed. In the study, several Nd:YAG capsulotomies led to dropouts in the round-edged IOL group. To solve the resulting missing value problem, the missing values were replaced by estimated PCO values in various scenarios; that is, different assumptions were made of how PCO would have developed without a capsulotomy. Standard statistical analyses that included the estimated PCO values rather than excluding the incomplete cases were then performed. Results The analysis of all cases (including the estimated PCO scores) showed a highly significant difference between the round-edged group and the sharp-edged group. Sensitivity analyses confirmed that the difference between the 2 groups remained significant up to highly implausible values chosen for the missing PCO scores, thus proving the correctness of the analysis. Conclusions This study showed it is possible to perform statistical analyses without excluding incomplete cases. This approach is recommended for all studies with Nd:YAG dropouts as it increases the statistical power. Excluding incomplete cases may lead to biased or wrong study conclusions.

This article was published in Journal of Cataract & Refractive Surgery and referenced in Journal of Clinical & Experimental Ophthalmology

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