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In my opinion, the Age-Related Eye Disease Study (AREDS) investigators promoted a nonsignificant result into a conclusive recommendation.1 Here is how they did it.
The primary study outcomes for AREDS are explicitly stated in the "Participants and Methods" section of the article: (1) progression to advanced age-related macular degeneration (AMD) and (2) a 15-letter decrease in visual acuity. These outcomes were to be evaluated in all patients by independent tests of significance of the 2 primary treatments. This carefully specified primary analysis led to 4 tests, none of which was statistically significant. One, testing the effect of zinc on progression to advanced AMD, achieved a level of significance defined by the investigators as suggestive.
Despite these negative results, the investigators recommend combined treatment with antioxidants and zinc based on their secondary analysis. Two analytic approaches provided them with significant results. First, the authors restricted the analysis to a subgroup. The mainstream practice of clinical trials warns that unless the main overall comparison is significant, investigators should be conservative in their interpretation of significant subgroup results.2 Second, they featured the combined treatment group, which in secondary analysis broke the boundary of statistical significance, thereby disregarding the primary analysis in which neither treatment was significant.
In its discussion of relevant literature, the "Comment" section is as selective as the analysis. At a planning meeting, the AREDS chairman recounted his efforts to review retinal photographs from the first published study of zinc and AMD3 and his disappointment at learning they had been lost shortly after publication. By this criterion alone the relevance of that small clinical trial is depleted. Nevertheless, the AREDS investigators report its finding to support their recommendation. Some major epidemiological studies that are not supportive, glancingly mentioned in the introduction, have no voice in the "Comment" section.
Adverse effects reported by the investigators include an increase in hospitalizations for urinary tract problems among participants treated with zinc and yellowing of the skin among participants taking antioxidants. They modified the protocol for current and former smokers during the course of the study because of published reports of increased mortality among smokers supplementing with beta carotene. Furthermore, they caution that the health effects of long-term use of their proposed treatment are unknown.
Analyses in clinical trials are complex endeavors. Austin Bradford Hill observed that the inferences we draw turn on our personalities.4 In an article in the New York Times, Gina Kolata spoke to public frustration at reports of clinical research that convert suggestive results to conclusive ones.5 A public that is concerned with AMD, physicians who need to advise and treat, and industry representatives who wish to provide us with products that are effective all depend on us to get it right in clinical research. In my opinion, the message that should have emerged from AREDS is that these treatments failed to demonstrate efficacy in preventing AMD and are not recommended for that use.
Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature
Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal
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