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Editors Selection IGR 7-2
Quality of clinical trials
Comment by Anne Coleman on:
12467 Quality of controlled clinical trials on glaucoma and intraocular high pressure, Llorca J; Martinez-Sanz F; Prieto-Salceda D et al., Journal of Glaucoma, 2005; 14: 190-195
Llorca et al. (734) and Schwenn et al. (736) are to be commended for addressing an important topic: the quality of clinical trials on glaucoma treatment. Although the articles have similar aims, their approaches are different. Llorca et al. searched seven international ophthalmology journals that have high impact factors and that are targeted to ophthalmic generalists. Schwenn et al. chose a list of 11 frequently read peer-reviewed journals which overlapped with only four of the journals chosen by the Llorca and co-authors. The choice of the journals clearly can make a substantial difference in the articles that are reviewed, as can the dates of eligible articles. Llorca included articles from January 1980 to January 1999, while Schwenn evaluated studies published between 1996 and 1999. The number of articles that were initially identified was mentioned by Llorca (349) but not by Schwenn. This information is useful because it gives the reader a perspective regarding how many articles were excluded from the evaluation for specific reasons such as that the trials were performed on animals or were not clinical trials. Llorca et al. used two masked reviewers with epidemiological skills to review the manuscripts, while Schwenn et al. do not describe reviewer characteristics or the extent to which the review protocol involved masking. Both studies listed the methodological criteria that were used to evaluate the manuscripts. One of the criteria Llorca used to evaluate clinical trials was the avoidance of analyses of subgroups, as if that was a desirable characteristic. Although the avoidance of subgroup analyses prevents researchers from capitalizing on chance to exaggerate the significance of findings, subgroup analyses can be used to help evaluate effect modification and to evaluate exploratory hypotheses, which may lead to future studies. Put simply, subgroup analyses are often of scientific interest. So long as a clear distinction is drawn between primary intent-to-treat analyses and secondary analyses, it would be a shame for investigators to halt all subgroup analyses. Schwenn emphasizes that studies should be of a long duration, pointing to the Advanced Glaucoma Intervention Study (AGIS) as an example. That said, even in a long-term investigation, not all publications are based on data from the entire period under study, for example, the AGIS investigators did not report their intention-to-treat results until the twelfth publication from the study, at which point the reported results showed no significant difference between the two treatment groups. Schwenn and co-authors conclude that guidelines for glaucoma clinical trials are necessary and recommend that these guidelines be developed by the Association of International Glaucoma Societies (AIGS). In line with this call to action, a set of guidelines was developed in 2004 by the AIGS and is posted on the AIGS website (http://www.globalaigs.org under Guidelines on Reporting and Publishing). The guidelines by CONSORT, which were recommended by Llorca et al. and the AIGS guidelines, represent an alternative framework. In clinical-trial settings where the key ingredients are similar, the kinds of safeguards advocated by both sets of authors offer an important foundation to strengthen the basis for insights from clinical research.
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